What imputed righteousness to Abraham?
Faith imputed righteousness to Abraham. As Abraham believed God, his faith was that which was credited as righteousness, and through him all the families of the earth would be blessed. Paul stipulates that as Abraham believed God, so believers are in that same position, with faith being the means of imputed righteousness.
Les explains that it was faith—Abraham's belief in God—that imputed righteousness to him. This is tied to Paul's stipulation that as Abraham believed God, so is where we are. The context then moves to Genesis chapter 3, where God makes a covenant with Adam after the fall, promising a Redeemer in verse 15: the seed of the woman who would bruise Satan's head, though Satan would bruise his heel. From that promise, the Abrahamic covenant is built, showing that through Abraham and his offspring the seed of the woman would come, and through him all the families of the earth would be blessed.