Verse 12 says:
Therefore, do not let sin reign in your mortal body, that you should obey it in its lusts.
Reign means to rule over like a king reigns over his kingdom.
Mortal body is talking about your flesh and bones ~ what makes up your human body.
Verse 13 says:
And do not present your members as instruments of unrighteousness to sin, but present yourselves to God as being alive from the dead and your members as instruments of rightousness to God.
Present (not present like a Christmas present, but present like you present a speech) is talking about a decision you make ~ a choice to do one thing or another.
Members is refering to your physical body parts.
Does that help? It's saying make a choice to keep your body under control and present it to God as an instrument of righteousness.
Much of this book has been about making choices!
So ~ what's the big deal? Does God really care if you keep yourself pure? Yes, He does. Remember He created us male and female and He created marriage and He created sex. He created it all ~ but He also gave us guidelines on how they should work. Page 164 and 165 list just a few of the verses explaining how God feels about these things.
Page 165 and 166 give a pretty detailed rundown of how God created our bodies and how it all works together, including a picture on page 167. {If any of this doesn't make sense, talk to your Mom or me!} It's important to understand how we are created because it goes along with the rest of the chapter.
A good part of the rest of the chapter spends time talking about just a few of the different sexually transmitted diseases. Now ~ you can read all that and say oh that will never happen to me. REALLY? How can you be so sure? I bet that's what everyone who already has an STD used to think too! You also have to consider if it's worth the risk. Page 169 compares the risk to playing Russian roulette ....
Just as the last chapters have talked about keeping yourself pure for the good of your future spouse, this chapter talks about waiting for the good of your future children. Is it worth risking them as well?
Children are a heritage from the Lord, the fruit of the womb is a reward. Like arrows in the hands of a warrior, so are teh children of one's youth. Happy is the man who has his quiver full of them. Psalm 127:3-5
