Isaac is a type of all evangelical, godly, humble, believing hearts. Isaac confessed that Abraham’s inheritance was not rightfully his by law (since Ishmael was older) but by grace, since God granted it to him out of special grace and appointed him as heir of Abraham’s possessions. All the blessed children of God do likewise. They confess possessions. All the blessed children of God do likewise. They confess that by nature they do not justly deserve heaven, but rather hell and condemnation. Yet they cling to God’s grace and take comfort in the Gospel’s gracious promise that the heavenly inheritance is given them for the sake of Jesus Christ’s merit and thus
they become children of God. For “to all who receive Him, to them the Lord Jesus gave the right to become children of God” (John 1:12); and “not all who are seed of Abraham are therefore his children, but ‘Through Isaac shall your seed be named,’ This means that they are not the children of God who are children of the flesh, but the children of the promise are counted as the seed,” says Paul (Rom. 9:[7-]8); and they “were born not of blood nor of the will of the flesh nor of the will of man but of God” (John 1:13). Here we see that no one can become a child of God and an heir of heaven through his natural birth, but only through true faith in Jesus Christ, who obtained God’s grace for us.
God’s grace and love alone avail
To blot out our transgression.1
And 1 John 1[:1] says, “Whoever believes that Jesus is the Christ is born of God.” And by such faith we too are accounted and reckoned true children of Abraham.
Isaac was born of the free princess Sarah who, unlike Hagar, knew no toil to speak of. Likewise, all blessed children of God are born of God to everlasting freedom, and they do not boast of their glorious works and hard labor. Rather, when we have done everything, we say, “we are unprofitable servants” {Luke 17:10].
Isaac let himself be mocked, reviled, and persecuted. Likewise, all evangelicals let themselves be hated and afflicted in the world for their faith and suffer through it all in Christlike patience.
Isaac founded his heart solely on God’s promise, using the words [2 Cor. 12:9], “Your grace, O Lord Jesus, is sufficient for me in this life and the one to come.” Like, all the blessed children of God, like the apostles in Acts 15:11, set their hearts only on Jesus’ grace and say with St. Paul, “Not because of works of righteousness that we did, but according to His own mercy He saved us” (Titus 3:5).
1 From the hymn “Aus tiefer Not schrei ich zu dir” (Luther, 1524), st. 2, lines 1-2; see LSB 607 “From Depths of Woe I Cry to Thee.”
Herberger, Valerius The Great Works of God: Parts Three and Four: The Mysteries of Christ in the Book of Genesis, Chapters 16-50 72-73