Greetings,

The faith of Christ is defined in the very same passage that it is used in.

Gal. 2:20 I am crucified with Christ: neverthless I live; yet not I, but Christ liveth in me: and the life which I now live in the flesh I live by the faith of the Son of God, who loved me, and gave himself for me.

The faith of Christ is defined simply as the faith that Jesus had. We all know through the scriptures that faith is an action word. Jesus' faith was that He loved us and gave Himself for us. We are instructed to have that same faith. This is the faith that Paul was living by when he lived in peril of his very life for the gospels sake and the churches that he had planted.

Peace