Genesis 21:1 And the Lord visited Sarah as He had said, and the Lord did for Sarah as He had spoken. 2 For Sarah conceived and bore Abraham a son in his old age, at the set time of which God had spoken to him. 3 And Abraham called the name of his son who was born to him—whom Sarah bore to him—Isaac. 4 Then Abraham circumcised his son Isaac when he was eight days old, as God had commanded him. 5 Now Abraham was one hundred years old when his son Isaac was born to him. 6 And Sarah said, “God has made me laugh, and all who hear will laugh with me.” 7 She also said, “Who would have said to Abraham that Sarah would nurse children? For I have borne him a son in his old age.” 8 So the child grew and was weaned. And Abraham made a great feast on the same day that Isaac was weaned.
"Few under the Old Testament were brought into the world with such expectations as Isaac. He was in this a type of Christ, that Seed which the holy God so long promised, and holy men so long expected. He was born according to the promise, at the set time of which God had spoken. God's promised mercies will certainly come at the time which He sets, and that is the best time. Isaac means laughter, and there was good reason for the name, ch. 17:17; 18:13. When the Sun of comfort is risen upon the soul, it is good to remember how welcome the dawning of the day was. When Sarah received the promise, she laughed with distrust and doubt... This mercy filled Sarah with joy and wonder. God's favours to his covenant people are such as surpass their own and others' thoughts and expectations: who could imagine that he should do so much for those that deserve so little, nay, for those that deserve so ill? Who would have said that God should send his Son to die for us, his Spirit to make us holy, his angels to attend us? Who would have said that such great sins should be pardoned, such mean services accepted, and such worthless worms taken into covenant?...” (Matthew Henry)
In the day of our visitation (Jesus' first coming), Yahweh had not yet given Abraham, nor his offspring, the heavenly Land (Acts 7:5). But He “led him throughout all the land of Canaan, and multiplied his descendants and gave him Isaac.” (Josh 24:3) The growth of Abraham's tent was evidence of increased spiritual seed, but the gift of Isaac pertained to physical seed. Isaac's birth was like a pledge of His power and ability. It testified of more physical descendants, as well as the inheritance of Land. Likewise, the gift of the Holy Spirit is pledge of our inheritance (Ephesians 1:13-14).
Genesis 21:8 So the child grew and was weaned. And Abraham made a great feast on the same day that Isaac was weaned. 9 And Sarah saw the son of Hagar the Egyptian, whom she had borne to Abraham, mocking.
"Perhaps v. 9 does not directly attach to v. 8, even though most commentators do connect the two. Yet nothing actually indicates that what Ishmael does is directly to be associated with the festivities of this day… Everything in this verse hinges on the translation of 'metsach (ch) eq', which we have rendered, 'was (always) mocking'— the ‘always' to cover the frequentative participle...The writer did not want to say that he mocked Isaac, because, apparently, Ishmael... ['was always mocking’] the prospects of Isaac and his spiritual destiny, in fact, just adopted a mocking attitude over against everything involved in Isaac’s future.” (H. C. Leupold)
10 Therefore she said to Abraham, “Cast out this bondwoman and her son; for the son of this bondwoman shall not be heir with my son, namely with Isaac.” 11 And the matter was very displeasing in Abraham’s sight because of his son.
Ishmael was put out to preserve the integrity of the congregation and perhaps “for the destruction of the flesh, that his spirit may be saved.” (1 Cor 5:5) "Because of the antipathy to spiritual treasures displayed by Ishmael, as indicated above, Sarah concludes that a radical cure of the evil should be taken in hand. The evil threatening is so grievous, and the damage it ultimately might do so alarming, that nothing short of expulsion of the Egyptian maid and her son can be deemed an adequate solution. True, Sarah refers only to the matter of sharing in the inheritance; but she evidently means this in the sense of sharing in the entire inheritance, which consists in spiritual as well as in physical assets. Else Gal 4:30 would hardly have deemed her words worthy of quoting with approval." (Leupold) "This was a type of the rejection of the unbelieving Jews, who, though they were the seed of Abraham, yet, because they submitted not to the gospel covenant, were... disfranchised...” (Benson Commentary) to provoke them to jealousy. (Rom 11:14)
12 But God said to Abraham, “Do not let it be displeasing in your sight because of the lad or because of your bondwoman. Whatever Sarah has said to you, listen to her voice; for in Isaac your seed shall be called. 13 Yet I will also make a nation of the son of the bondwoman, because he is your seed.”
"Now the error into which the Galatian churches fell, was the introduction of that which addressed itself to nature. 'Except ye be circumcised after the manner of Moses, ye cannot be saved.’" (C. H. Mackintosh's Notes) In the end, he concluded that circumcision is nothing and uncircumcision is nothing, but a new heart is what is important. (Galatians 6:15) So this is an allegory of religion. "The son of the bond-woman… might become a great nation, he might dwell in the wilderness, and become an archer, he might become the father of twelve princes, but he was the son of the bond-woman all the while. On the contrary, no matter how weak and despised Isaac might be, he was the son of the free-woman. His position and character, his standing and prospects, were all from the Lord. 'That which is born of the flesh is flesh; and that which is born of the Spirit is spirit.’ [“And you brethren, like Isaac, are children of promise.” Gal 4:28] Regeneration [is needed,] not a change of the old nature, but the introduction of a new; it is the implantation of the nature or life of the Second Adam, by the operation of the Holy Ghost, founded upon the accomplished redemption of Christ, and in full keeping with the sovereign will or counsel of God. The moment a sinner believes in his heart, and confesses with his mouth, the Lord Jesus, he becomes the possessor of a new life, and that life is Christ. He is born of God, is a child of God, is a son of the free-woman. (See Rom10:9; Col 3:4; 1 John 3:1-2; Gal 3:26; 4:31)” (C. H. Mackintosh's Notes)
14 So Abraham rose early in the morning, and took bread and a skin of water; and putting it on her shoulder, he gave itand the boy to Hagar, and sent her away. Then she departed and wandered in the Wilderness of Beersheba. 15 And the water in the skin was used up, and she placed the boy under one of the shrubs. 16 Then she went and sat down across from him at a distance of about a bowshot; for she said to herself, “Let me not see the death of the boy.” So she sat opposite him, and lifted her voice and wept.
Yahweh had spoken. So, “he proceeds with all singleness of heart and denial of self to dismiss the mother and the son. This separation from the family of Abraham was, no doubt, distressing to the feelings of the parties concerned. But it involved no material hardship to those who departed, and conferred certain real advantages. Hagar obtained her [once sought] freedom. Ishmael, though called a lad, was at an age when it is not unusual in the East to marry and provide for oneself. And their departure did not imply their exclusion from the privileges of communion with God, as they might still be under the covenant with Abraham, since Ishmael had been circumcised, and, at all events, were under the broader covenant of Noah. It was only their own voluntary rejection of God and his mercy, whether before or after their departure, that could cut them off from the promise of eternal life. It seems likely that Hagar and Ishmael had so behaved as to deserve their dismissal from the sacred home.” (Barnes' Notes)
17 And God heard the voice of the lad. Then the angel of God called to Hagar out of heaven, and said to her, “What ails you, Hagar? Fear not, for God has heard the voice of the lad where he is. 18 Arise, lift up the lad and hold him with your hand, for I will make him a great nation.” 19 Then God opened her eyes, and she saw a well of water. And she went and filled the skin with water, and gave the lad a drink. 20 So God was with the lad; and he grew and dwelt in the wilderness, and became an archer. 21 He dwelt in the Wilderness of Paran; and his mother took a wife for him from the land of Egypt.
"The fortunes of Ishmael. God cares for the wanderers. He hears the voice of the lad, whose sufferings from thirst are greater than those of the mother... [The] Angel [of the Covenant] is sent, who addresses Hagar in the simple words of encouragement and direction... Lay thy hand firmly upon him. The former promise Genesis 16:10 is renewed to her. God also opened her eyes that she saw a well of water, from which the bottle is replenished, and she and the lad are recruited for their further journey. It is unnecessary to determine how far this opening of the eyes was miraculous. It may refer to the cheering of her mind and the sharpening of her attention. In Scripture the natural and supernatural are not always set over against each other as with us. All events are alike ascribed to an ever-watchful Providence, whether they flow from the ordinary laws of nature or some higher law of the divine will. 'God was with the lad.' Ishmael may have been cured of his childish spleen...'He became an archer.’... Paran lay south of Palestine, and therefore on the way to Egypt, out of which his mother took him a wife. The Ishmaelites, therefore, both root and branch, were descended on the mother's side from the Egyptians.” (Barnes' Notes)
Genesis 21:22 And it came to pass at that time that Abimelech and Phichol, the commander of his army, spoke to Abraham, saying, “God is with you in all that you do. 23 Now therefore, swear to me by God that you will not deal falsely with me, with my offspring, or with my posterity; but that according to the kindness that I have done to you, you will do to me and to the land in which you have dwelt.”
Abimelech was a righteous man and his was a righteous nation. They followed Yahweh God of Abraham. He had already been a believer but the true and living God had recently come to him in a dream and told him that Abraham was a prophet and not to harm him... and to restore his wife to him. He "therefore moves for an oath to be taken by him, which he knew would be sacred and binding to Abraham,...; perhaps he had heard that God had promised to give the whole land of Canaan to him and his posterity, and among the rest his kingdom, which was a part of it; and, seeing him grow great and powerful, he could not tell how soon it might be ere he was put in the possession of it, whether in his own time, or his son's, or his grandson's; and therefore desires Abraham that he would swear to do no hurt to them whenever it should be: but according to the kindness I have done unto thee, thou shalt do unto me, and to the land wherein thou hast sojourned; that, as he had given him full liberty to sojourn in any part of his kingdom where he pleased, so, when the whole country should come into his possession, that he, or his son, or his grandson, in whatsoever time it should be, might quietly enjoy their own land, and all the inhabitants of it; at least that they might not be driven out of it, but sojourn in it as he had done.” (John Gill)
24 And Abraham said, “I will swear.”
"Here a proof of the promise (Ge 12:2) being fulfilled, in a native prince wishing to form a solemn league with Abraham. The proposal was reasonable, and agreed to [Ge 21:24].” (Jamieson-Fausset-Brown)
25 Then Abraham rebuked Abimelech because of a well of water which Abimelech’s servants had seized.
"Before he swore and entered into covenant with him, he thought it advisable to inform him of an affair that had happened concerning a well of water, which in those hot and dry countries, as the southern parts of the land of Canaan were, was an affair of great importance; and to make complaint of the ill usage of Abimelech's servants with respect to it, and to reason with him about it, that the thing might be adjusted to mutual satisfaction, and so a firm basis and foundation be laid for the continuance of friendship for the future; which was wisely done before their league and covenant was ratified: this it seems was a well.” (John Gill)
26 And Abimelech said, “I do not know who has done this thing; you did not tell me, nor had I heard of it until today.”
27 So Abraham took sheep and oxen and gave them to Abimelech, and the two of them made a covenant. 28 And Abraham set seven ewe lambs of the flock by themselves.
29 Then Abimelech asked Abraham, “What is the meaning of these seven ewe lambs which you have set by themselves?”
30 And he said, “You will take these seven ewe lambs from my hand, that they may be my witness that I have dug this well.” 31 Therefore he called that place Beersheba, because the two of them swore an oath there.
32a Thus they made a covenant at Beersheba.
Seven ewe (female) lambs…. this being a sin offering (Lev 4:32) and seven representing perfection, this represents perfect union and forgiveness among brethren. It was thus established that Abraham dug this well.
As concerning the covenant: "And to show that he was fully satisfied with Abimelech's answer to his complaint, as well as willing to enter into covenant by sacrifice [the way of Yahweh], when such creatures were divided, and the covenanters passed between the pieces, for so it follows: and both of them made a covenant; or, 'cut or struck a covenant'; cut the sacrifice in pieces and passed between them, in token of the compact and agreement they entered into with each other; signifying that whoever broke it deserved to be cut in pieces as those creatures were." (John Gill)
32b So Abimelech rose with Phichol, the commander of his army, and they returned to the land of the Philistines.
33 Then Abraham planted a tamarisk tree in Beersheba, and there called on the name of the Lord, the Everlasting God.
"Jehovah is called the everlasting God, as the eternally true, with respect to the eternal covenant, which He established with Abraham (Genesis 17:7). The planting of this long-lived tree, with its hard wood, and its long, narrow, thickly clustered, evergreen leaves, was to be a type of the ever-enduring grace of the faithful covenant God.” (Keil & Delitzsch Commentary)
34 And Abraham stayed in the land of the Philistines many days.
"Abraham, being now in a good neighbourhood, stayed a great while there. There he made, not only a constant practice, but an open profession of his religion. There he called on the name of the Lord, as the everlasting God; probably in the grove he planted, which was his place of prayer. Abraham kept up public worship, in which his neighbours might join. Good men should do all they can to make others so. Wherever we sojourn, we must neither neglect nor be ashamed of the worship of Jehovah.” (Matthew Henry)