Did you ever notice how the gospels tend to emphasize what man must do, while St. Paul in his letters and epistles emphasizes what God does?
An interesting way to look at it is that God (Jesus) emphasizes man's role while man (Paul) emphasizes God's role. Not that there aren't overlaps; Jesus says that with man this is impossible but with God all things are possible and Paul gives a long list of behaviors that will preclude entrance into the Kingdom. But that doesn't negate the general tone.
It sort of reminds me of the old cliche that we should work as if everything depended on us and pray as if everything depended on God.