Genesis 17:21

Gen 17:21 But my covenant will I establish with Isaac, which Sarah shall bear unto thee at this set time in the next year.

Ver. 21. But my covenant.] This is the thirteenth time that the covenant is named in this chapter, saith an interpreter; and hereby is meant the promise of Christ and salvation by him. A subject so sweet to every sanctified soul, that St Paul cannot come off it. He names the Lord Jesus Christ ten times together in ten verses. {1Co 1:1-10} It was to him Mel in ore, melos in aure, iubilum in corde .{ a}

{a} Bernard.

John Trapp, A Commentary or Exposition upon All the Books of the Old and New Testament (1647–1656) — public domain. Text from a community e-Sword module.

Gen_17:21

My covenant will I establish with Isaac

Isaac, a type of Christ

1.

He is born in a miraculous manner. He was the child given by promises, and came not in the ordinary course of nature. So Christ was long promised and miraculously born.

2. He was the son of the house, while all others were his servants. So the position of Christ in the heavenly household was made by His birth. No circumstances could alter His relationship to that household. He was there by a natural necessity. Others may come and go, but the Son abides.

3. He was the progenitor of a free race. Isaac was the son of the free woman, and the ancestor of a great and free people. Christ makes men free when they are born into the kingdom of God by His spirit, and thus belong to that holy nation whose children walk in perfect liberty.

4. He was the channel of blessing to all nations. Christ was the life and power which gave effect to that blessing. He was that blessing itself.

Isaac, a type of the regenerate man

1. He was born by a distinct act of the will of God. So the regenerate man becomes Gods child, not by the course of nature, but by a special grace. He is eminently born of God.

2. He was free born. So each child of God is made free from all bondage. He needs not the commands of law to compel him to obedience, for he obeys from love of his Father. Thus Isaac was the type of the evangelical dispensation, as Ishmael was that of the legal.

The Biblical Illustrator, edited by Joseph S. Exell (c. 1880s–1900s) — public domain. Text from a community e-Sword module.

Gen 17:21. He names that child Isaac, that is, laughter, because Abraham rejoiced in spirit when this son was promised him.

Joseph Benson's Commentary on the Old and New Testaments (1811–1818) — public domain. Text from a community e-Sword module.

Verse 21. My covenant will I establish with Isaac] All temporal good things are promised to Ishmael and his posterity, but the establishment of the Lord's covenant is to be with Isaac. Hence it is fully evident that this covenant referred chiefly to spiritual things-to the Messiah, and the salvation which should be brought to both Jews and Gentiles by his incarnation, death, and glorification.

Adam Clarke's Commentary on the Bible (1810–1826) — public domain. Text from a community e-Sword/MySword module.

But my covenant will one establish with Isaac,.... The covenant of circumcision; for though Ishmael was circumcised, and his posterity practised that rite, yet it was not enjoined them of God; nor was it to them, or served the same purpose as to the Israelites; and particularly the promise of the land of Canaan, made in that covenant, belonged only to the posterity of Isaac, and to those only in the line of Jacob, and especially that of the Messiah springing from him, which circumcision had a respect unto:

whom Sarah shall bear unto thee, at this set time, in the next year: that is, at the end of nine months, which is the set time a woman goes with child.

John Gill's Exposition of the Whole Bible (1746–1763) — public domain (CC PDM 1.0). Text via the HelloAO Bible API.

The covenant of the promised Seed to come out of his loins, and of life and salvation to accrue to himself and to his posterity by virtue of that Seed; in comparison whereof God speaks slightly of all the temporal blessings conferred upon Ishmael, though in themselves they were great and glorious. By which it may sufficiently appear that Abraham’s faith, whereby he is said to be justified, Rom 4:1-25, had a further reach in it than to his own immediate child, even to the Messias, whose day therefore Abraham is said to have seen, Joh 8:56.

Matthew Poole's English Annotations on the Holy Bible (1683–1685) — public domain. Text from a community e-Sword/MySword module.

But my covenant will I establish with Isaac, whom Sarah shall bear unto thee at this set time in the next year (cf. Gen_21:2)

The Pulpit Commentary (1880–1919), ed. H.D.M. Spence-Jones & Joseph S. Exell — public domain. Text from a community e-Sword module.

He names that child, Isaac - Laughter, because Abraham rejoiced in spirit when this son was promised him.

John Wesley, Explanatory Notes Upon the Whole Bible (1754–1765) — public domain. Text via the GEBible commentary corpus.

למועד הזה "at this time." (anniversary). We do not know precisely on what date G'd had granted Avraham this prophetic vision.

בשנה האחרת. G'd informs Avraham that a year will elapse between the time he received this message and its realization. It is as if the Torah had written that Sarah would give birth at this time in the following year. He did not tell him when she would become pregnant, nor the length of time of her pregnancy. Our sages in Rosh Hashanah 10 assume that the birth occurred on Passover (the date on which Passover would occur in the future) seeing that Sarah became pregnant on Rosh Hashanah.

Radak on the Tanakh — English translations: “Sefaria Community Translation” (CC0 1.0 (public-domain dedication)); “Eliyahu Munk, HaChut Hameshulash” (CC BY 4.0); “Rabbi Mike Feuer, Jerusalem Anthology” (CC BY 4.0); and “R. David Kimhi on the first book of Psalms, Translated by R.G. Finch, London, 1919” (public domain). Text via Sefaria.