Our forefathers understood the difference between law and grace and the appropriate place and time to use both.
18th Century preachers would preach clearly the law of God, the holiness of God, and the justice of God to people who felt very little conviction of sin. Jonathan Edwards used his message "Sinners in the Hands of an Angry God" to awaken a slumbering community to their sin and rebellion towards their Creator.
However, our forefathers also understood that it was essential to preach to the believers in Christ the eternal, immeasurable grace of God. Why? People who had already felt their sin needed to be shown the Savior in all His glory and beauty.
Today churches get the use of law and grace confused. For some reason we try to get the lost to feel comfortable at church, and then when they feel the church is a comfortable place, we ask them to join. But to keep them committed to Christ we then have to give them the law, "do this or miss out on God's blessing."
How sad. We should make sinners feel as uncomfortable as possible under the expositional teaching of the Scripture (because Scripture does the same thing), but we should do our very best to show convicted sinners the unconditional, eternal, and unbelievable blessings of grace found in casting one's trust on the person and work of Jesus Christ.
If a person has truly tasted of grace wild horses could not keep him from serving.
So, tell your lost friends the truth about the law of God with a spirit of grace and humility, but to that soul who has obtained by faith the righteousness of Jesus Christ, do your very best to show him all the understanding, love and grace you possibly can, even if he or she is radically different from you in lifestyle, personality, and gifts. His righteousness through faith in Christ is the same righteousness you have received by faith.
There is no room for legalism in the church. But we need a ton of law in the world.
Grace to you and yours,