Sin was before the law of Moses. It was the same during Moses time, and it is still sin now. Justification by faith doesn’t negate what sin is, in fact, it verifies that sin exist. If sin does’t exist, we don’t nee to be justified.
Justification by faith changes your starting place. It changes the platform we start from. Instead of working to be right with God, He makes us right with Him through Jesus. From the position of being made righteous, we are to bear the fruit of righteousness. We are to do righteous deeds, not to obtain righteousness, but because we have been made righteous with God. Fruit grows until it is mature. We are to grow, not in righteousness, but in bearing the fruit of righteousness. We see the kind of fruit righteousness is in Galatians 5:22–26: the fruit of the spirit.
By the power of the new birth, and help of the Holy Spirit, we are to display an outward working of an inward power.
Stay strong and prepared!