That's why context is important and has to be taken into consideration.
Demons believe, but are not saved. You maintain that you must continue to believe to remain saved, yet belief doesn't save you.
Jesus saves you. If you believe in Him, you can be reborn, and receive new life, His life, not just your own life.
Belief doesn't save you, Jesus saves you. He does this by immersing you into Himself to share in all He has, INCLUDING His faith, the faith of Christ.
So you graduate. From your initial belief in the truth of the Gospel, to the faith of Christ in you.
Your believing after that is one of two things.
Either your believing is the manifestation of Jesus Christ in you, and your believing is the faith of Christ being revealed through you.
OR,
Your believing is your own doing, something you yourself do, apart from Christ, and, well, we all know how inconsistent people are in their moods and thoughts from day to day.
This is the significance of the "faith of Jesus Christ". It's not yours, it's His. We are inconsistent, but Jesus Christ, the same yesterday, today, forever!
He doesn't change.
Much love!