I think that a lot of people are in the opinion that using the Law in witnessing means being a judgmental or condemning Christian. Let me tell you that that is the farthest thing from the truth. I can't tell you the love that you feel for the lost when you're around people who utilize the Law in evangelism. What you have to realize is that you are not judging anyone when you open up God's Law, the 10 Commandments. You don't need to worry that Matthew 7:1-6 will apply to you when it says judge not lest you be judged because that is not what biblical evangelism is about. Its about using the Law as a mirror to the person's soul to show them that they've broken God's Commandments. There's no finger pointing, no saying the person is sinner without showing them why. It's simply, lovingly, opening up the Law to them and showing them that there will be judgment for breaking God's Law and their need for the Savior, Jesus. As far as not wanting a non-believer to feel condemned I just have to say, "really?" A smoke alarm going off in someone's house doesn't condemn them, they are already condemned to burn if they don't heed it's warning. The smoke alarm simply tells of the impending danger and gives the person the choice to flee from the fire that is to come. If they don't flee to salvation from the flames, they will perish. Remember John 3:18 says-"Whoever believes in him is not condemned, but whoever does not believe stands condemned already because he has not believed in the name of God's one and only Son." You can see that sinners are already condemned, why not warn them to repent, or turn from their sin and run from the fires of Hell to the loving arms of Jesus. Don't be judgmental, or condemning, and especially don't be arrogant. Just lovingly share the Gospel, the full Gospel in faithfulness to God's commands. Be the smoke alarm and warn someone of the dangers today!!
Psalm 19:7 (King James Version)
7The law of the LORD is perfect, converting the soul: the testimony of the LORD is sure, making wise the simple.