Romans 1:17 (NKJV) " For in it the righteousness of God is revealed from faith to faith; as it is written, "The just shall live by faith."
We begin our life in Christ by faith and we continue to live by faith that is why Paul quotes an Old Testament verse, " The just shall live by faith."
In Hebrews 11:6 is says," But without faith is is impossible to please Him(God)..." Whatsoever is not of faith is sin. Any walk that is less than the walk of faith is a sinful walk." Our Christian life is made of faith walking. If it is not then we are not obeying the Lord Jesus. Stop right here and ask yourself," Am I walking by faith or by sight?" Which one is it? Will you believe God's great promises for an invisible future or cling to the visible present?