You've gotten it exactly backwards. It's Roman Catholics who believe that works (refraining from sin) independent of faith (proclaiming they are saved) is the path to salvation. Protestants reject that and believe that salvation comes as a result of divine grace & is unconditonal, regardless of the sins, "mortal" or otherwise, they have committed on this earth. Most African-Americans in this country are Protestants & what you describe is in fact compatible with their Protestantism.
Well I think you have Protestant theology confused. In any case, I go by what the Bible says.
The Catholic Church teaches that salvation is impossible without Sanctifying Grace, which is received by Faith. It also teaches that grave sin is a rejection of Sanctifying Grace. Thus, those who commit grave sin cannot be saved.
But the Church does NOT teach that “works” can cause salvation.