We were created to be Christ-like and to be Him on Earth. We are supposed to continue His works, spreading the message of love and peace and to live by Faith that we are saved by His grace. Paul is saying basically that even our belief in God does not start within ourselves. It is a gift from God so we as Christians cannot take pride in our positions as Christians. When I say Pride, I mean the boastful pride. The deadly sin of Pride.
Everything we are, everything we have, is a gift, a precious gift, from God.
That is what that passage means to me.