There are several levels that I want to answer this question on. On a theoretical kind of level, self injury is a sin. In the Bible the apostle Paul tells us this:
“Do you not know that your body is a temple of the Holy Spirit within you, whom you have from God? You are not your own, you were bought with a price. So glorify God in your body.” (1 Corinthians 6:19-20)
Do you see what’s going on here? Paul is saying that if you are a Christian then God’s spirit lives in your body. You no longer belong to yourself, which means that you don’t have the right just to do whatever you want. Instead, the thing to do ‘in your body’ is glorify God.
That being said, I suspect you probably knew that self-harm was a sin deep down. God doesn’t make up arbitrary rules and impose them on us for fun! The rules God puts in place are there for our own good. Like a father keeps his toddler away from the kitchen because they will burn or poison themselves, God makes rules for us and life just works better if we follow them. God does this because he loves you.
That’s really the first thing to note: God loves you. Very, very much - so much in fact that He was willing to let his Son die for you. I don’t know whether you are asking this question for yourself, or a friend. But if someone you know is injuring themselves then its important that they know that God loves them too. God doesn’t want them to hurt themselves, because he cares very much for them and wants what is best for them. He wants them to be one of his children, and he wants to protect them and look after them.
Self harm is a sign that something is very wrong. People who self harm do so because the process and the pain gives them relief from the mental pain and anguish they are under, its a way of dealing with their problems in the short term solution but does not deal with it in the long term. Usually people who self harm need to seek help from professionals who can help them talk through and work out the causes fro their anguish. There is nothing to be ashamed about in this - many people suffer in the same way and think that they are all alone in dealing with it but they are not!
Can I encourage you to find a Christian friend you can talk to about this in real life? Do you go to church? Can you trust your minister enough to ask this same question to him? How about a teacher at school? If you don’t know anyone then there are several free telephone numbers you can call, just to talk these kind of issues through. You might like to try the kids help line if you are in Australia: 1800 55 1800. It seems to me that this is the kind of question that is best discussed with someone face to face or on the phone, rather than over the internet.
Thanks Zack, I hope I was able to help out a little.