The Bible teaches two great doctrines, the law and the gospel. The law tells us what to do, and in that function it makes us aware that we have not lived up to God’s perfect standards. The gospel tells us what God has done for our salvation. Both need to be proclaimed. Witnessing to Muslims includes speaking both law and gospel in love.
The Law Shows Our Sin
The law declares what God’s will is. It includes the commands—all the things we are to do or not to do, in thought, word, deed.