knowing that a man is not justified by works of law, but through the faith of Christ Jesus, and we have believed into Christ Jesus, in order that we may be justified by faith of Christ, and not by works of law, because by works of law no flesh shall be justified.

Then was the law against the promises of God? it could not be so. For if the law was given being able to create life, truly justification would have been by law:

Behold I Paul say unto you, that, if you may be circumcised, Christ shall profit you nothing.

for being ignorant of God's righteousness, and seeking to establish their own righteousness, they have not submitted to the righteousness of God.

and if by grace, it is not at all by works: since in that case grace is no more grace.

Then indeed if perfection was through the Levitical priesthood, for unto it the people have been tithed, what need is there still that another priest shall rise after the order of Melchizedek, and not be called after the order of Aaron?

Christ

by which you are also saved; which word I preached to you, if you hold it fast, otherwise you believed in vain.

General references

For if I again build the things which I have destroyed, I constitute myself a transgressor.