And Abraham called the name of his son that was born unto him, whom Sarah bare to him, Isaac.

Scofield Reference Notes

[1] Sarah

Sarah, type of grace, "the freewoman," and of the "Jerusalem which is above." See Gen 17:15-19 Gal 4:22-31

[2] Isaac is typical in fourfold way:

(1) of the Church as composed of the spiritual children of Abraham Gal 4:28.

(2) of Christ as the Son "obedient unto death" Gen 22:1-10 Phil 2:5-8.

(3) of Christ as the Bridegroom of a called-out bride see Gen 24; also, "Church," Mt 16:18, See Scofield Note: "Mt 16:18".

(4) of the new nature of the believer as "born after the Spirit" Gal 4:29.

Jamieson-Fausset-Brown Bible Commentary

3, 4. Abraham called the name of his son . Isaac . and circumcised-God was acknowledged in the name which, by divine command, was given for a memorial (compare Ge 17:19), and also in the dedication of the child by administering the seal of the covenant (compare Ge 17:10-12).

Matthew Henry's Concise Commentary

21:1-8 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. When God gives us the mercies we began to despair of, we ought to remember with sorrow and shame our sinful distrust of his power and promise, when we were in pursuit of them. 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? A short account of Isaac's infancy is given. God's blessing upon the nursing of children, and the preservation of them through the perils of the infant age, are to be acknowledged as signal instances of the care and tenderness of the Divine providence. See Ps 22:9,10; Ho 11:1,2.