Our 8th emphatic belief states that "in the New Covenant, we walk by faith in God's promises, not by Moses' law". This is a point of contention we have with some of the language in the Westminster Confessions, which repeatedly speaks of the law as the believer's binding rule of life (WCF XIX.6; LC Q# 93, 97; SC #40). By "law", they mean "moral law", an extra-biblical term. When the Apostle Paul speaks of "the law", he means "Moses' covenant". This seems like hair-splitting, but God's Word informs us directly as to our rule of life, and we seek to use His language.
We can't call the law our rule of life. The law made nothing perfect, but the bringing in of a better hope did. The promise to Abraham was not through the law, but through the righteousness of faith. In fact, if the inheritance be of the law, it is no more of promise. Paul boldly states that the law is not of faith, and that the law is not made for a righteous man.
You probably know that by grace are ye saved through faith, that both Jews and Gentiles are justified by faith, we have access by faith into this grace wherein we stand and are all the children of God by faith in Christ Jesus. It was unbelief, a life void of the rule of faith, which condemned many Jews, who sought righteousness not by faith, but as it were by the works of the law.
In addition, we are sanctified by faith in Christ Jesus, who is made unto us sanctification. Consider Hebrews 11's list of Old Testament saints who lived victoriously by faith. When New Testament (NT) believers in Galatia started to revert to Moses' covenant, Paul asks are ye so foolish? Having begun in the Spirit, are ye now made perfect by the flesh?
The Bible tells us our rule of life: we walk by faith and not by sight. Paul, expert in Moses' law, said the life which I now live in the flesh I live by the faith of the Son of God, who loved me, and gave Himself for me. If ever there was a place to say, "Christians live by the law", he would have said so. We live by faith, stand by faith, and walk by faith. You will not find these phrases in the NT: "live by law", "stand by law", or "walk by law". Of course, if you preach this, men will accuse you of antinomianism (just like Paul was). As we said before, we do not make void the law by faith, but establish it.
Christians ask, "What would Jesus do?", not Moses.