For therein is the righteousness of God revealed from faith to faith: as it is written, The just shall live by faith.
Romans 1:17 (KJV)
The just are called to live by faith. This means we agree with what God has said about us, we believe the promises of God for our lives. We are not moved by what we can see in the natural or feel in our emotions, we are moved only by the Word of God! We live by faith because faith enables what is already true about us in Christ to manifest in our day to day lives.