As a historical figure in the Bible, Isaac, like Abraham, does not represent a complete, spiritually mature man. He represents only a part of the experience and life of a spiritually mature person, which includes the inheriting of grace, not using one’s own effort, and the restful enjoyment of the riches of Christ. When he was old, he blessed Jacob blindly (Gen. 27:1-29). This proves that he was not sufficiently mature in his spiritual life and that he was not a complete, spiritually mature person, but can be considered only a part of such a person, just as we saw previously concerning Abraham.
Ishmael was born of Abraham according to the flesh, through his concubine, Hagar, unto slavery. When Isaac grew and was weaned, Ishmael mocked him. Consequently, Ishmael and Hagar were cast out by Sarah, and Ishmael was not allowed to be heir along with Isaac. Thus, Ishmael signifies those who keep the law by their self-effort, those who are under slavery and are born according to the flesh. They will be cast out from the inheritance of grace and will not be able to inherit and restfully enjoy God’s grace as an inheritance with those who are born of grace.
Isaac was born of Abraham according to promise, through Abraham’s wife, Sarah, and he became the unique seed who inherited all the riches of his father. He also inherited the promise given to Abraham concerning Christ, in whom all the nations of the earth would be blessed. When Isaac had grown up and was weaned, Ishmael began to mock him. Furthermore, Isaac was offered as a burnt offering and thus experienced death and resurrection. Thus, Isaac represents the New Testament believers, who are born to be sons of God according to the Holy Spirit by God’s grace and who become God’s heirs, inheriting and restfully enjoying God’s possessions; who suffer persecution from those who are born according to flesh; and who are offered to God as a burnt offering, thereby experiencing death and resurrection. When Isaac was old, he blessed Jacob blindly. This proves that he was not sufficiently mature in his spiritual life and that he was not a complete, spiritually mature person, but can be considered only a part of such a person.