# For this reason

"So"

# it is by faith

The word "it" refers to receiving what God had promised. Alternate translation: "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

Here "the promise may rest on grace" represents God giving what he promised because of his grace. Alternate translation: "so that what he promised might be a free gift" or "so that his promise would be because of his grace" (See: [[rc://en/ta/man/translate/figs-metaphor]])

# 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

This refers to those who have faith as Abraham did before he was circumcised. Alternate translation: "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. (See: [[rc://en/ta/man/translate/figs-inclusive]])