Mormons are much more accustomed to talk about keeping the commandments than talking about sin. We therefore encourage you to focus the discussion on the commandments – especially our inability to keep them. This jives with one of the main reasons God gave the commandments (the law), namely, to make us aware of our sinfulness.
Therefore by the deeds of the law there shall no flesh be justified in his sight: for by the law is the knowledge of sin
Romans 3:20
This passage shows that God’s commandments are not rungs on a ladder helping us get to heaven, as Joseph Smith explained them. (This is also what all people, by nature, think.) Rather, they make us conscious of our sinfulness. As we come face to face with the commandments’ high standards, we realize we have fallen far short of keeping them. Rather than being rungs on a ladder, they are like mirrors which help us see our sinfulness.
It is vitally important to keep this purpose clearly in mind. When people don’t, they have the tendency to water the commandments down. “God doesn’t really mean all worry is a sin.” “God wasn’t really serious when he commanded us to be perfect”. Such attempts are not only untrue; they also dull the commandments’ effectiveness. Keep them sharp. Let them cut sharply.
For the word of God is living and active. Sharper than any double-edged sword, it penetrates even to dividing soul and spirit, joints and marrow; it judges the thoughts and attitudes of the heart
Hebrews 4:12
This applies to all of God’s commands, not just the Ten Commandments. Every single divine command is a tool the Holy Spirit uses to convict people of their sins. Especially devastating are the commands demanding positive actions like loving everybody including our enemies, or being content in all situations, or blessing those who curse us.
Hold up God’s commands as mirrors. Don’t let Mormons brush the commandments off as unimportant. Don’t let them weaken their message. Use the commandments to show them how sinful they are and the deep trouble they are in because of their sin. It is the loving thing to do.