Saul disobeys God and doesn't kill all the Amalekites (1 Sam 15).
David is anointed and Saul tries to kill him (1 Sam 16-21).
Saul kills all the priests and inhabitants of Nob (1 Sam 22).
When you reject God's anointed, you end up rejecting His people, too.
One way to tell how you are doing with the Lord is to consider how you are treating His people.