Mormons and good works
The Bible says that "without faith it is impossible to please God" (Heb 11:6). Mormons do a lot of good works. Are any of their works pleasing to God? What will happen to them if they die Mormon?
As the passage you cited explains, and as Romans 14:23 teaches (“…everything that does not come from faith is sin.”), only Christians can perform good works. Only people who are led to trust in Jesus Christ alone for their salvation can do things—out of love for God and in accordance with his word—that are pleasing to God. People outside the Christian Church may do nice things and good things in the eyes of others, but their actions are not good works because those actions come from hearts lacking saving faith.
Mormon theology is not a saving message. Any religion based on work righteousness is void of biblical truth and leads its followers down the path to eternal destruction. Mormons and others who are caught in the web of work righteousness need to know and believe the truths of the Bible: that people enjoy salvation only through Spirit-worked faith in Jesus Christ and not by the deeds they perform in life (Acts 16:30-31; Romans 3:21-31; 4:5; Ephesians 2:8-9).
You can learn more about Mormon theology and how better to witness to Mormons by visiting the website of Truth in Love Ministry.