Well, I'll congratulate you because you're the first Catholic who hasn't tried to skirt this issue. Where precisely did you get your faith from?
My faith is a gift from God. I have inherited it through my Baptism in Christ. Like any inheritance, I can choose to throw it away, to reject it through neglect.
I'm not assured of maintaining faith until my dying breath, and thus I am not assured of salvation until I stand before Christ and hear my judgment. Works do not merit me salvation, but they make me a caretaker of my faith and a co-operater with Christ in helping others to their own salvations. Jesus will not preserve our faith if we don't want it. We receive grace through good works and reception of the sacraments. As much grace as we can receive, the stronger our faith. When we reject opportunities of grace, that gift of faith begins to shrink. If we're not careful (working out our salvation in fear and trembling) that faith could be gone without us even knowing it.