There is no such thing as an unfaithful Christian. A Christian by definition is someone who is faithful. A person who is not faithful to Christ is by definition not a Christian. We are people who exercise faith in Christ Jesus. We believe in Jesus and have put our life in his hands completely. We trust Jesus no matter what happens to us in life. No matter how much prosperity and pleasure we enjoy or how much pain and suffering we endure, we trust Jesus. This shows us that being faithful means that we continue to obey Jesus. We do what Jesus says, not the world. We hold on to the faith (the scriptures, the revealed word of God) that has been delivered to the world. The faith is our anchor for faith. Paul stated this point another way when he wrote to the Romans.
For in it the righteousness of God is revealed from faith for faith, as it is written, “The righteous shall live by faith.” (Romans 1:17 ESV)
The Christian lives by faith. The Christian does not live by sight. The Christian lives his or her life completely believing in the plan, purposes, and care of God. Paul quoted from the prophet Habakkuk when he taught how Christ is the revealing of the righteous faithfulness of God. When Habakkuk was told that his people were going to be invaded, captured, and killed because of their sins, God’s answer to Habakkuk when Habakkuk did not understand was, “The righteous live by faith.” The faithfulness of God generates our faith in him. Our faith in God does not come from empty space. Our faith comes from the precious promises of God who cannot lie and keeps all he has purposed.