Let a man examine himself.
It's a familiar phrase in Lutheran circles - from 1 Corinthians 11, dealing with proper reception of the Lord's Supper - but also how we end up viewing confession and absolution. Examine yourself. The Greek is "δοκιμαζέτω" - Let one test one's self, approve after scrutiny as fit for an office -- Liddel and Scott have lots of things on it which you can find here. But there is that idea of self-examination.
There are few things more dangerous than the simple assumption that you yourself are right because your outward actions are right. This is a major theme of the Jesus' preaching in the Gospels.
"You cleanse the outside of the cup and of the dish, but inside you are full of greed and wickedness."
"Woe to you, for you build the tombs of the prophets your fathers killed."
"You did not enter yourself, but you hindered those who were entering."
"I tell you, this man went down to his house justified, rather than the other."
So on and so forth.
As Christians we are to examine our motivations, so that we do not hide behind a veneer of righteousness - to see that we do not act in a way that only appears or seems to be right. We know that a little leaven leavens the whole lump, that the outward wickedness first starts in the heart and proceeds from there... that great shame and vice is an outgrowth of the unchecked wickedness of the heart.
So we are called to examine. Examine our own motives. To test ourselves, to prove ourselves. Are we righteous, moral agents, or are we those who must ride constant herd not merely upon outward actions, but upon a guileful heart?
And yet - how quickly I will become defensive when someone questions my motives. Why should I, for I know that I am sinful and wretched. God be merciful to me, the sinner!