For body-modified Christians like myself, here is a helpful answer from the Q&A of the Lutheran Missouri Synod (a.k.a. the good guys) that emphasizes the difference between the moral law and the ceremonial law.
I[t] should be kept in mind that the prohibition in Leviticus 19:28–“Do not cut your bodies for the dead or put tattoo marks on yourselves. I am the Lord”–belongs to Old Testament levitical or ceremonial law–which has been set aside or annulled with the coming of Christ (Col. 2:16-17; Acts 15). Leviticus is full of such laws, including the command one verse earlier: “Do not cut the hair at the sides of your head or clip off the edges of your beard.”
It falls into the “weaker brother” category from Romans 14. Of course we don’t want to offend our brothers. But there are levels of appropriateness in terms of avoiding offense. For example, if you have a visible tattoo, say, on your neck, and the only way to cover it up is to wear a scarf or turtleneck, in the summer… the more appropriate way brothers to deal with offense might be to deal with prejudice and legalism in the weaker brother instead. If such a one is offended by a Christian with body modifications, is this person going to be crippled from being able to minister to unbelievers downtown or in the soup lines?
Martin Luther wrote in his commentary on Galatians, “This difference between the Law and the Gospel is the height of knowledge in Christendom.” As church leaders, whenever we have the opportunity to stifle legalism, perfectionism, and man-made religion, we owe it to our beloved church to take that step. As covenant theology types, we believe the Gospel preached by Christ and his Apostles was the same message of salvation given by God in covenant to Abraham and David, who put their trust in the Messiah who was to come. We know that “by the works of the law no one will be justified,” but Scripture also says if we love him, we will obey his commands. We are told all over the New Testament to pursue righteousness, to be obedient, and to avoid sin, and the moral law is where God defines righteousness and sin. So we want to do all we can to make sure we understand the difference between God’s binding moral law (his commands), and the temporary, localized ceremonial laws of the Old Testament, so that we can spur one another on toward sanctification and yet not burden each other with burdens too hard to bear.