3:29 How are we to understand this?

This sums up Paul's teaching in chapter 3 that believers are justified by faith, not by the works of the law (cp Ga 3:1-5).

As Abraham was justified by faith in God, so too believers are justified by faith in Christ, and are blessed, like Abraham (cp Ga 3:6-9).

The law could not save - it only condemned, but Jesus rescued all who want to be saved, by His atoning blood. He became a curse, in fulfilment of scripture, that all who accept Him by faith are redeemed from the curse (cp Ga 3:10-14).

God covenanted for Gentiles to be justified by faith before the law came down, therefore the law cannot void the covenant and make its promises to Abraham ineffective (cp Ga 3:15-18).

The purpose of the law was to keep sinful man in the way of salvation until Abraham's seed - Christ - came (cp Ga 3:19-23).

The law pointed to Christ as the supreme sacrifice who would justify all who came to Him by faith, whether they be Jews, Gentiles, slaves, free men, males or females. They would all become children of God through Christ - the heirs of Abraham, and the inheritors of God's covenanted promise (cp Ga 3:24-29).