English Standard Version (ESV)
17 But if you call yourself a Jew and rely on the law and boast in God 18 and know his will and approve what is excellent, because you are instructed from the law; 19 and if you are sure that you yourself are a guide to the blind, a light to those who are in darkness, 20 an instructor of the foolish, a teacher of children, having in the law the embodiment of knowledge and truth— 21 you then who teach others, do you not teach yourself?
While you preach against stealing, do you steal? 22 You who say that one must not commit adultery, do you commit adultery? You who abhor idols, do you rob temples? 23 You who boast in the law dishonor God by breaking the law. 24 For, as it is written, “The name of God is blasphemed among the Gentiles because of you.”
Just this morning I was telling my son that he needs to be sure that he's seated while he eats. I did this while I was standing up eating a pancake. Great parenting, eh? I'm sure he didn't notice...
We do this all the time. We say one thing, even though we may be doing the exact opposite. Often, we're not doing this on perfect, we just don't think about our own lives.
What Paul is trying to encourage us to do is recognize our own faults. We need to see ourselves as sinners who have received untold grace from God Almighty. When we realize how we were lost and have been found, we are awash in gratitude towards God, and this changes the way we see the world. Rather than self-righteous people who need to convict the world of their sin, we go forth as sinners who have been brought back to forth, as grateful people with a story to tell and Good News to share.
So realize the depth of your sin. Realize that God's forgiveness is much, much greater than your sin. Be grateful. Share your gratitude. May the Good News of Jesus Christ ring from every mountain!