How do Isaac and Ishmael function as types of grace and law?
Isaac, the son of promise, functions as a type of grace. Ishmael, the son of the flesh, functions as a type of law; Paul in Galatians depicts him as a picture of law. Together they illustrate the contrast between promise/grace and flesh/law.
Les teaches that Isaac is by type a picture of grace because he was the son of promise, while Ishmael was the son of the flesh and is depicted by Paul in Galatians as a picture of law. A type is a perfect illustration of a New Testament truth, as seen with Abraham as the man of faith or Joseph as a type of Christ. In Genesis 24, Abraham sending his servant to get a bride for Isaac is a perfect parallel of the Holy Spirit calling out the bride for Christ, though Les calls it a good illustration rather than a perfect type due to one detail.
For it is written, that Abraham had two sons, the one by a bondmaid, the other by a freewoman.