Christians are believers in Christ and they have faith in His teachings.
Here is how a Bible dictionary defines faith:
Faith means abandoning all trust in one's own resources.
Faith means casting oneself unreservedly on the mercy of God.
Faith means laying hold on the promises of God in Christ, relying entirely on the finished work of Christ for salvation, and on the power of the indwelling Holy Spirit of God for daily strength.
Faith implies complete reliance on God and full obedience to God.
Now faith is the substance of things hoped for, the evidence of things not seen.