Charles Ellicott Commentary John 8:39

"They answered and said unto him, Our father is Abraham. Jesus saith unto them, If ye were Abraham`s children, ye would do the works of Abraham." — John 8:39 (ASV)

They answered and said to him, Abraham is our father.—They feel the meaning which has not yet been expressed , and claim the descent from Abraham which He has already allowed (John 8:37).

If you were Abraham’s children, you would do the works of Abraham.—Almost all the better manuscripts read, “If you are,” for “If you were.” This must mean, “If you are Abraham’s children—but the supposition is excluded, for you would do the works of Abraham, and this is opposed to fact.” They are the physical seed of the patriarch, but they are not the ethical children, for the true child would bear the moral impress of the father which would be seen in his works. The thought of the previous verse is again present here.

The distinction between “seed” and “children” is another instance of an idea which we encounter in this section, and was developed in the writings of St. Paul. (Compare to Romans 9:7 and following).