While watching a documentary on Vince Lombardi I learned that he was a staunch Roman Catholic who at one time thought about joining the priesthood. Obviously he did not but, according to the documentary, he wanted to invest truth and goodness in people. He did so by coaching. His players are his lasting testimony to the good he did in others.
I reasoned that only God could put a desire to do good for others in a person. Being Roman Catholic it is likely that Lombardi thought his good deeds would earn him God's favor. Lombardi said as much. We Protestants "protest" saying that no man can earn God's favor. It is only by God's grace in the sacrifice of Jesus on the cross that can satisfy God's wrath and offer a person forgiveness and eternal life. I believe that. But...because it is by God's grace that we are saved I don't have to believe it is by grace alone that I am saved. Not having a full understanding of the atonement of Jesus cannot get a person damned otherwise a person could be saved by right knowledge (which is a work) and not by grace.
There are plenty of reasons to hold on to the truth of Salvation by Grace Alone. The first is that to not do so would eventually lead away from the atoning work of Jesus all together and thus not believe in Jesus as Savior. That will damn a person.
Personally I would never, ever say a person is damned for not understanding correctly the doctrine of grace. That would be ungracious. I thank God for people like Vince Lombardi. May God have mercy on his soul!