en_tn_condensed/rom/04/16.md

it is by faith

"it is by faith that we receive the promise" or "we receive the promise by faith"

in order that the promise may rest on grace

"so that what he promised might be a free gift"

those who are under the law

This refers to the Jewish people, who were obligated to obey the law of Moses.

those who share the faith of Abraham

"those who believe as Abraham did"

father of us all

Here the word "us" refers to Paul and includes all Jewish and non-Jewish believers in Christ. Abraham is the physical ancestor of the Jewish people, but he is also the spiritual father of those who have faith.