Biblical Commentary on the Old Testament, by Carl Friedrich Keil and Franz Delitzsh, [1857-78], at sacred-texts.com
Birth of Isaac. - Jehovah did for Sarah what God had promised in Gen 17:6 (cf. Gen 18:14): she conceived, and at the time appointed bore a son to Abraham, when he was 100 years old. Abraham gave it the name of Jizchak (or Isaac), and circumcised it on the eighth day. The name for the promised son had been selected by God, in connection with Abraham's laughing (Gen 17:17 and Gen 17:19), to indicate the nature of his birth and existence. For as his laughing sprang from the contrast between the idea and the reality; so through a miracle of grace the birth of Isaac gave effect to this contrast between the promise of God and the pledge of its fulfilment on the one hand, and the incapacity of Abraham for begetting children, and of Sarah for bearing them, on the other; and through this name, Isaac was designated as the fruit of omnipotent grace working against and above the forces of nature. Sarah also, who had previously laughed with unbelief at the divine promise (Gen 18:12), found a reason in the now accomplished birth of the promised son for laughing with joyous amazement; so that she exclaimed, with evident allusion to his name, "A laughing hath God prepared for me; every one who hears it will laugh to me" (i.e., will rejoice with me, in amazement at the blessing of God which has come upon me even in my old age), and gave a fitting expression to the joy of her heart, in this inspired tristich (Gen 21:7): "Who would have said unto Abraham: Sarah is giving suck; for I have born a son to his old age." מלּל is the poetic word for דּבּר, and מי before the perfect has the sense of - whoever has said, which we should express as a subjunctive; cf. Kg2 20:9; Psa 11:3, etc.
Expulsion of Ishmael. - The weaning of the child, which was celebrated with a feast, furnished the outward occasion for this. Sarah saw Ishmael mocking, making ridicule on the occasion. "Isaac, the object of holy laughter, was made the butt of unholy wit or profane sport. He did not laugh (צחק), but he made fun (מצחק). The little helpless Isaac a father of nations! Unbelief, envy, pride of carnal superiority, were the causes of his conduct. Because he did not understand the sentiment, 'Is anything too wonderful for the Lord?' it seemed to him absurd to link so great a thing to one so small" (Hengstenberg). Paul calls this the persecution of him that was after the Spirit by him that was begotten after the flesh (Gal 4:29), and discerns in this a prediction of the persecution, which the Church of those who are born after the spirit of faith endures from those who are in bondage to the righteousness of the law.
Sarah therefore asked that the maid and her son might be sent away, saying, the latter "shall not be heir with Isaac." The demand, which apparently proceeded from maternal jealousy, displeased Abraham greatly "because of his son," - partly because in Ishmael he loved his own flesh and blood, and partly on account of the promise received for him (Gen 17:18 and Gen 17:20). But God (Elohim, since there is no appearance mentioned, but the divine will was made known to him inwardly) commanded him to comply with Sarah's demand: "for in Isaac shall seed (posterity) be called to thee." This expression cannot mean "thy descendants will call themselves after Isaac," for in that case, at all events, זרעך would be used; for "in (through) Isaac shall seed be called into existence to thee," for קרא does not mean to call into existence; but, "in the person of Isaac shall there be posterity to thee, which shall pass as such," for נקרא includes existence and the recognition of existence. Though the noun is not defined by any article, the seed intended must be that to which all the promises of God referred, and with which God would establish His covenant (Gen 17:21, cf. Rom 9:7-8; Heb 11:18). To make the dismissal of Ishmael easier to the paternal heart, God repeated to Abraham (Gen 21:13) the promise already given him with regard to this son (Gen 17:20).
The next morning Abraham sent Hagar away with Ishmael. The words, "he took bread and a bottle of water and gave it to Hagar, putting it (שׂם participle, not perfect) upon her shoulder, and the boy, and sent her away," do not state the Abraham gave her Ishmael also to carry. For ואת־היּלד does not depend upon שׂם and ויּתּן because of the copula ו, but upon יקּח, the leading verb of the sentence, although it is separated from it by the parenthesis "putting it upon her shoulder." It does not follow from these words, therefore, that Ishmael is represented as a little child. Nor is this implied in the statement which follows, that Hagar, when wandering about in the desert, "cast the boy under one of the shrubs," because the water in the bottle was gone. For ילד like נער does not mean an infant, but a boy, and also a young man (Gen 4:23); - Ishmael must have been 15 or 16 years old, as he was 14 before Isaac was born (cf. Gen 21:5, and Gen 16:16); - and השׁליך, "to throw," signifies that she suddenly left hold of the boy, when he fell exhausted from thirst, just as in Mat 15:30 ῥίπτειν is used for laying hastily down. Though despairing of his life, the mother took care that at least he should breathe out his life in the shade, and she sat over against him weeping, "in the distance as archers," i.e., according to a concise simile very common in Hebrew, as far off as archers are accustomed to place the target. Her maternal love could not bear to see him die, and yet she would not lose sight of him.
Then God heard the voice (the weeping and crying) of the boy, and the angel of God called to Hagar from heaven, "What aileth thee, Hagar? Fear not, for God hath heard the voice of the boy, where he is" (באשר for אשׁר בּמקום, Sa2 15:21), i.e., in his helpless condition: "arise, lift up the lad," etc. It was Elohim, not Jehovah, who heard the voice of the boy, and appeared as the angel of Elohim, not of Jehovah (as in Gen 16:7), because, when Ishmael and Hagar had been dismissed from Abraham's house, they were removed from the superintendence and care of the covenant God to the guidance and providence of God the ruler of all nations. God then opened her eyes, and she saw what she had not seen before, a well of water, from which she filled the bottle and gave her son to drink.
Having been miraculously saved from perishing by the angel of God, Ishmael grew up under the protection of God, settled in the wilderness of Paran, and "became as he grew up an archer." Although preceded by יגדּל, the רבה is not tautological; and there is no reason for attributing to it the meaning of "archer," in which sense רבב alone occurs in the one passage Gen 49:23. The desert of Paran is the present large desert of et-Tih, which stretches along the southern border of Canaan, from the western fringe of the Arabah, towards the east to the desert of Shur (Jifar), on the frontier of Egypt, and extends southwards to the promontories of the mountains of Horeb (vid., Num 10:12). On the northern edge of this desert was Beersheba (proleptically so called in Gen 21:14), to which Abraham had removed from Gerar; so that in all probability Hagar and Ishmael were sent away from his abode there, and wandered about in the surrounding desert, till Hagar was afraid that they should perish with thirst. Lastly, in preparation for Gen 25:12-18, it is mentioned in Gen 21:21 that Ishmael married a wife out of Egypt.
Abimelech's Treaty with Abraham. - Through the divine blessing which visibly attended Abraham, the Philistine king Abimelech was induced to secure for himself and his descendants the friendship of a man so blessed; and for that purpose he went to Beersheba, with his captain Phicol, to conclude a treaty with him. Abraham was perfectly ready to agree to this; but first of all he complained to him about a well which Abimelech's men had stolen, i.e., had unjustly appropriated to themselves. Abimelech replied that this act of violence had never been made known to him till that day, and as a matter of course commanded the well to be returned. After the settlement of this dispute the treaty was concluded, and Abraham presented the king with sheep and oxen, as a material pledge that he would reciprocate the kindness shown, and live in friendship with the king and his descendants. Out of this present he selected seven lambs and set them by themselves; and when Abimelech inquired what they were, he told him to take them from his hand, that they might be to him (Abraham) for a witness that he had digged the well. It was not to redeem the well, but to secure the well as his property against any fresh claims on the part of the Philistines, that the present was given; and by the acceptance of it, Abraham's right of possession was practically and solemnly acknowledged.
From this circumstance, the place where it occurred received the name שׁבע בּאר, i.e., seven-well, "because there they sware both of them." It does not follow from this note, that the writer interpreted the name "oath-well," and took שׁבע in the sense of שׁבעה. The idea is rather the following: the place received its name from the seven lambs, by which Abraham secured to himself possession of the well, because the treaty was sworn to on the basis of the agreement confirmed by the seven lambs. There is no mention of sacrifice, however, in connection with the treaty (see Gen 26:33). נשׁבּע to swear, lit., to seven one's self, not because in the oath the divine number 3 is combined with the world-number 4, but because, from the sacredness of the number 7, the real origin and ground of which are to be sought in the number 7 of the work of creation, seven things were generally chosen to give validity to an oath, as was the case, according to Herodotus (3, 8), with the Arabians among others. Beersheba was in the Wady es-Seba, the broad channel of a winter-torrent, 12 hours' journey to the south of Hebron on the road to Egypt and the Dead Sea, where there are still stones to be found, the relics of an ancient town, and two deep wells with excellent water, called Bir es Seba, i.e., seven-well (not lion-well, as the Bedouins erroneously interpret it): cf. Robinson's Pal. i. pp. 300ff.
Here Abraham planted a tamarisk and called upon the name of the Lord (vid., Gen 4:26), the everlasting God. Jehovah is called the everlasting God, as the eternally true, with respect to the eternal covenant, which He established with Abraham (Gen 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.
Abraham sojourned a long time there in the Philistines' land. There Isaac was probably born, and grew up to be a young man (Gen 22:6), capable of carrying the wood for a sacrifice; cf. Gen 22:19. The expression "in the land of the Philistines" appears to be at variance with Gen 21:32, where Abimelech and Phicol are said to have returned to the land of the Philistines. But the discrepancy is easily reconciled, on the supposition that at that time the land of the Philistines had no fixed boundary, at all events, towards the desert. Beersheba did not belong to Gerar, the kingdom of Abimelech in the stricter sense; but the Philistines extended their wanderings so far, and claimed the district as their own, as is evident from the fact that Abimelech's people had taken the well from Abraham. On the other hand, Abraham with his numerous flocks would not confine himself to the Wady es Seba, but must have sought for pasture-ground in the whole surrounding country; and as Abimelech had given him full permission to dwell in his land (Gen 20:15), he would still, as heretofore, frequently come as far as Gerar, so that his dwelling at Beersheba (Gen 22:19) might be correctly described as sojourning (nomadizing) in the land of the Philistines.