There are phrases you never say until you're a parent. (The titular quote came from my wife's lips recently.) I wonder how many of God's words we don't understand for that reason. God is building His family and, as a father, has had to set and alter the rules to form His children in the right way.
We're hearing the word from His lips but not always understanding the reason behind them. Jesus was not always completely understood, even by His closest followers and friends. The mind of God - the intellect behind the words - is impossible for our finite brains to handle. If we cannot understand that mind, we are left with trust - with faith. Thankfully, understanding is not necessary. We are the child being told what to do, and, even if we don't understand it or agree with it, we obey because Dad said so. Because He is right, even if we don't understand why yet.