It is not enough to "believe in" Jesus. In fact, I'm sure most 'Christians' "believe in" Jesus meaning they acknowledge the facts of the Gospel. So does Satan, so do demons. We are saved by FAITH not by belief!
Faith is a personal trust in the living and risen Christ who died for the sins of the world. It is trusting him and him alone as the only atonement for your wickedness, it is trusting him and him alone for your only hope of holiness and eternal life. It is a living, day by day personal relationship with the creator of the universe. Such a living faith results in a progressive sanctification, a growing in holiness and a dying to self, an increasing conformity to the likeness of Christ.
Christianity is a supernatural spiritual bond between fallen humans and the Almighty thrice holy God, through Christ, in which evil creatures like ourselves are transformed into "little Christs" more and more day by day until the day we die or the world ends, whichever comes first.
Yes, but we need to be careful here. Our works and our efforts do not contribute to our salvation, yet our holiness is the result of a genuine saving faith. It is a personal relationship. If we truly love Christ, will we continue to pursue the things he hates, the sins for which he suffered the wrath of God on the cross? No, not at all. We may stumble and fall, but we will no longer live for the darkness of this world if we've truly seen the light.