Every word that proceeds from the mouth of God. Every word that Saul was told that God wanted for him to do. You know I can see this happening to me in Saul's place. I am not very detailed oriented, likely because of this I may not make a good king. However, when it is someone important, we are likely to pay closer attention to what they want of us. In this case, this is a checklist that Saul should have had written down and cross off as it has been done.
Instead, Saul or someone else had a 'good idea' to save the best so that they could be sacrificed unto the Lord. Which in most cases would probably have been a great idea. However, in this case, it went against God's word and will. This is where we get a great context for the saying 'To obey is better than to sacrifice'.
I know that this is a challenge for me, I am not so good with details of God's word and it is all there written down for me. I really need to take the time to study it and to know it so I am not caught in a 'good idea' without first considering what God says about it.