Galatians 2:20-21
I have been crucified with Christ; it is no longer I who live, but Christ who lives in me; and the life which I now live in the flesh I live by faith in the Son of God, who loved me and gave Himself for me. I do not set aside the grace of God; for if righteousness comes through the law, then Christ died in vain.
These verses in Galatians are very important for us to understand. Paul tells us in 2 Cor 5:17, we are a new creation, Christ living in me, freed from the power of the sinful life (not leading a sinless life, but freed from the power). The quoted part makes very certain that we do not gain righteousness from our own works (... coming from the law ...). We only gain our righteous standing before the Father through the finished work of Jesus Christ, not of our own deeds. If this not the case, then His work was without merit, that is, in vain. This is an easy idea to speak in words, but human pride stands in the way to make execution to the fullest extent a challenge.