Things done in halves are never appreciated in the human circles. If something is to be done, then it must be done well with a touch of excellence. Same applies to our relationship with God. God expects us to wholly take His word and walk in it. Total obedience is the key to a healthy successful Christian life.
The prophet in the scripture reading did not fully obey the instructions given to him. He relayed the message to King Jeroboam with its accompanying signs. Yet, he allowed himself to be swayed by an old prophet who has lost touch with God.
He disobeyed God by not following exactly what God told him to do. This led to his shameful premature death. His life and ministry was cut off. Partial obedience is a sin and as such mars our relationship with God. This makes us vulnerable to the devil.
Partial obedience is disobedience; disobedience is a sin.