First you understand what God wants us do.
First God says true us. Later God says, if you do a mistake, what you do.
For example;
Do not kill anyone. But if you do, God says you if you murder a human what you will do. And if someone killed any other, what you do to him.
God says you "do not declare war". But same God says you "if you war with a people, what you must to do". Because you are on true way or you are on a wrong way God wants you do the true on new ambiance.
Another example: "Do not steal". God says you as a main order. But God says you when you stealed something what you must to do. God shows you way. But this don't permit you to steal. Because the main order is "do not steal". God's showing you a way after you do a steal don't shows to steal is true.
If you understand my last example, then you understand why God said which animals you can eat or which you can't. God says you "don't kill". But if you kill something, someone, then God says you what you can do.
I hope i told what i think this time.