The Mosaic Law/Teaching is of two:
1. The Letter (2:11-13)
2. Conscience (2:14-16)
Neither one can ever justify because:
a) God requires moral perfection (Matthew 5:20 & James 2:10)
b) Man is rebelliously sinful by nature (Romans 5:12-16 & 8:6-7)
c) And God will not overlook his sins, nor will He count his good works (Isaiah 64:6)
Even to say that we can do just one thing for our salvation would still add a yoke no one can keep (Acts 15:1, 10).
Thus. we're saved only by Faith Alone and nothing else (Ephesians 2:8-9).
And to still insist in adding to His work on the cross (Hebrews 9:12), is to denigrate His sacrifice (Galatians 2:21), and to fall from grace (Galatians 5:4).