If you look at the 10 commandments and understand what it is, it will show you how a Christian is supposed to look like. It will give you a value system, a basis for building your life.
This, together with the vertical axis, gives us the cross.
They speak much deeper things to us as believers.
Because that is what we are supposed to be.
Your life is an expression of how He defines us through the 10 commandments.