Blaspheming God's Name
"As it is written, 'The name of God is blasphemed among the Gentiles because of you.'"
Judaism in the first century was a complex religion wherein each different subgroup had its own perspective on what the true expression of God's covenant with Moses looked like. Pharisees equated their oral traditions with Scripture. Sadducees wanted to appease Rome, and they built doctrine only on the Pentateuch (Genesis–Deuteronomy). Zealots believed that a violent revolution against their pagan Roman occupiers would bring God's kingdom. Essenes withdrew to the wilderness, living as ascetics and producing the Dead Sea Scrolls.
Despite their differences, these groups agreed that ethnic Jewishness conferred a privileged status. The Apostle Paul agreed that Jewishness has its advantages (Rom. 3:1–2; 9:4– 5) but rejected the belief that Jews alone had the Lord's commandments and led virtuous lives (2:1–16). Merely possessing the clearest revelation of God's standards—the Mosaic law—cannot make one righteous before our Creator. If one seeks to be justified, or declared righteous, by the commandments, one must keep them perfectly. Even one "insignificant" failure will doom us (v. 13; see Gal. 3:10–12; 5:3; James 2:10).
"Minor" sins were bad enough, but even "big" sins such as theft, adultery, and idolatry were evident in the Jewish community (Rom. 2:17–23). First-century Jews were not rank idolaters who bowed to statues, so Paul connects their idolatry to robbing temples (v. 22). This could refer to the use of precious metals from pagan sanctuaries, not paying the Jerusalem temple tax, or something else entirely. The point is that first-century Jews tolerated idolatry and other sins, having learned nothing from their exile (2 Chron. 36). With few exceptions, they were not lights to the world, and consequently, the Gentiles were blaspheming God (Rom. 2:24). Such an idea was unthinkable to Paul's Jewish contemporaries, but he quotes Scripture to prove they were giving Gentiles cause to blaspheme the Lord.
Paul cites Isaiah 52:5, wherein the nations of Isaiah's era, because they conquered the God of Israel's people, blasphemously questioned His power to save. Yet exile was the people's fault, not the Lord's. Their sin led God to remove His protective hand, allowing the Gentiles to conquer the Jewish nation and, not knowing that exile was Yahweh's punishment for sin, blaspheme Him. Something similar happened in the first century. Many Gentiles admired Jewish ethics, but others saw the Jews not practicing what they preached and asked, "How great is Yahweh if the Jews live no more virtuously than anyone else?"
Coram Deo
The Bible is clear that until we are glorified, we will always fail at some level to practice what we preach. Non-Christians will take advantage of this and always use our failures as cause to blaspheme the Lord, and there is not much we can do about it. However, if we are open about our failures and are careful to never promise sinlessness in this life, we can render their criticisms wholly illegitimate. Christians are not free of hypocrisy, but we should be free of impenitent hypocrisy.