In 1 Samuel 15 we read of the telling of God rejecting Saul as king over Israel. I can not help but think how often I have done the "same" thing, though I was never king over anything and haven't ever gone into battle, I have done almost all that the Lord has told me to do.
God is serious about obedience; instant and complete. God wants us to listen and obey more than anything we can sacrifice. As a kids I only would think of sacrifice as literally a sacrifice of an animal. We don't sacrifice animals anymore, but there are sacrifices we can make, but that is not God's choosing. He wants us to obey His Word; He wants us to listen. We must be in the Word to listen and know it to obey.
Can you imagine being Samuel, having to tell the king that God rejected him? Can you imagine Saul's thoughts at this time? We must be on our knees following as closely to The King as we are able and pray that He keeps us ever closer.