Much of the Proverbs contrasts the wicked (i.e., those who do not reverence God) with the upright who fear Him (cf. Proverbs 1:7). This Proverb is no different. Even when slandered by neighbors who have no reverential fear of God, and therefore lack since (v.12), those who fear Him navigate their circumstances so as to avoid entrapment (v.9) because they know the will of God (e.g., Jesus). They realize all vengeance belongs to God, He seeks out retribution in due time. The upright avoid retaliation and are saved (cf. Deuteronomy 32:35-36). The correlation between the influence of righteousness and wickedness is not restricted to the interpersonal relationships shared between neighbors, but extends to the community and beyond.
The city rises or falls on its influence and attitudes toward righteousness and wickedness. The city rejoices when good things happen to deserving people. But wickedness ultimately brings it to ruin and no one mourns when evil people get their just deserts. By the influence of righteous people a city is exalted. The city benefits when it seeks to be governed in righteousness. But it suffers the consequences of godless rule when it allows wickedness to go unchecked. Righteousness exalts a nation, but sin is a reproach to any people (Proverbs 14:34). There is a way that seems prudent to men but without God’s direction that way ends in destruction (cf. 14:12; 16:25).
Verse 13 provides the concluding thought: Slanderers cannot be trusted with confidential matters. In contrast, trustworthy people know when to keep things private. Wisdom dictates prudence regarding the people with whom you choose to share confidential matters.
That God calls Christians to be children of the light does not license us to expose every intimate thing. Some matters are better left for God to handle in His sovereignty. Wisdom knows when to speak up and when to keep silent, everything has its proper timing (Ecclesiastes 3:1). A word fitly spoken is like apples of gold in a setting of silver (Proverbs 25:11), they indicate trustworthiness and beauty. If you are perplexed as to whether or not to speak up — pray! God still gives wisdom to those who fear Him (cf. James 1:5). Your trustworthiness is on the line.