You who boast in the law dishonor God by breaking the law. (ESV)
There is a major difference between those who are truly righteous and those who are self-righteous. Those who are truly righteous look at the perfect Law of God and they are brought to their knees. They realize that God's holy requirements are so foreign to their wicked heart that they cry out to God and ask for forgiveness and help.
Those who are self-righteous are naive enough to think that somehow they are good in themselves and are thereby capable of keeping God's righteous laws. Instead of being humbled by the law they are full of pride and arrogance, trusting in themselves without asking God to forgive them and help them to please Him.
Paul says in this verse that those who are boasting in the law are dishonoring God. Why? Because they are breaking his law. They want all the credit for righteousness, but they are incapable of it. When they do fall, God is dishonored. Think about it for a moment. It's the phonies in the church who give the church a bad name, not those who are humble recipients of God's grace.
If man was naturally obedient to the law then every occasion in Scripture where we find man encountering a holy God we would find him boldly standing before the throne, fully confident in his righteousness. Is that what we find? Not even close. Every occasion in Scripture where man meets God we find fear and a keen awareness of sinful disobedience to God's holy standard.
What kind of a person are you? Are you self-righteous? Or are you truly righteous? I pray that you will humble your heart before a holy God and ask for forgiveness through Christ. He will certainly answer your prayer.