How do believers enter into salvation according to Paul's example of Abraham?

Believers enter salvation by faith alone, just as Abraham was saved by faith plus nothing. Abraham had no law, sacrifice, or circumcision; he simply did what God said. Paul uses Abraham to show that Gentiles are not made Jews but enter in the same way—through faith apart from those works.

Les explains that in Romans 4:1 Paul comes back to Abraham, one of the Old Testament characters Paul alludes to more than anyone else. Abraham was saved by faith plus nothing: he did not sacrifice, practice circumcision, or have law; he simply did what God said. Les connects this to believers, noting that although Galatians calls those of faith children of Abraham, that does not make a Gentile a Jew—a Gentile remains a Gentile, and salvation does not make a Jew out of anyone. The point is that just as Abraham was saved without law, sacrifice, or circumcision, so believers also enter in by faith alone, which is why Paul uses Abraham repeatedly.

Romans 4:1

What shall we say then that Abraham our father, as pertaining to the flesh, hath found?

Why does Paul refer to Abraham so often?

Paul refers to Abraham frequently because Abraham was saved by faith plus nothing—before law, sacrifice, or circumcision—so he serves as the pattern for all who enter salvation by faith alone. Paul uses him to show that children of faith are Abraham's children without Gentiles becoming Jews.