“For Abraham had two kinds of children, children born of the promise, like Isaac, and other children born without the promise, as Ishmael. With this argument Paul squelched the proud Jews who gloried that they were the children of God because they were the seed and the children of Abraham. Paul makes it clear enough that it takes more than an Abrahamic pedigree to be a child of God. To be a child of God requires faith in Christ.
VERSE 24. Which things are an allegory.
Allegories are not very convincing, but like pictures they visualize a matter. If Paul had not brought in advance indisputable arguments for the righteousness of faith over against the righteousness of works this allegory would do little good.”