Whether you believe you can or not is ....... belief in yourself. That's faith. Believing that something CAN be achieved and that ... YOU can DO it!
That's totally different from believing in someone else ... and THEIR ability to do something FOR you.
Paul's gospel was that God had ENABLED the individual to do things ... through the apparent failure of his son ... and then the TRIUMPH of his son. In Paul's perception then, belief in Jesus Christ was ONLY to facilitate the FAITH in one's self to do the same things that had already been done by Jesus. Once you know that something CAN be done and HAS been done .... there's no more doubt that it can be done. Therefore, you can do it too.