There are two wrong ways that people commonly think about how to get into heaven. The first is what Protestants accuse us Catholics of, called works-righteousness. According to this idea, we do good things and bad things and God keeps track, and then if the good is more than the bad we get into heaven. This is what many people, Catholic and Protestant, tend to believe. It is wrong. We are not saved by works of the law. The other wrong way is the traditional Protestant teaching that they get from misreading these verses, called Sola Fide. According to this idea, if a person believes that Jesus is Lord then they will get into heaven no matter what they have done. Jesus himself says that this is wrong.
The true Catholic teaching is what St. Paul gives in this reading today: “By grace you have been saved.” Salvation is by grace alone. What is grace? “It is not from you; it is the gift of God.” It is the power of God to change us. We do not go to heaven by having more good actions than sins. We do not go to heaven because of what we happen to believe. We go to heaven if the grace of God changes us into the sort of people who can live in heaven. The reason why Protestants accuse Catholics of works-righteousness is that good works are one way to tell whether the grace of God is active in my life. If today I am more likely than last year to serve the poor and do the other things that Jesus says, then I clearly have changed for the better. There is progress in the right direction.
Also, because of free will, when we choose to do bad things, we are refusing the grace of God and not changing for the better. This is why no one can say that they have done enough good to get by with a little sin. Like the man in the Gospel today, when he decided to tear down his barns instead of sharing his bountiful harvest with the poor, it made him a little smaller and worse. Faith is important. “By grace you are saved through faith.” Knowing about Jesus and his teachings helps us to accept the grace of God, but knowing and even believing mean nothing if we are not changed for the better by them.