Do not cover their guilt, and let not their sin be blotted out from your sight, for they have provoked you to anger in the presence of the builders.
Sanballat and Tobiah grew furious because they feared what a walled Jerusalem would become: strong and formidable against them. Their scorn was malice dressed up as mockery, yet it backfired. They despised the work as foolish and beneath serious opposition, so they delayed their attacks until the Jews had already made too much progress to be stopped.
AI summary
Commenting on Nehemiah 4:1-6
And cover not their iniquity, and let not their sin be blotted out from before thee,.... Let it not go unpunished, and even let it not be pardoned; which is spoken, not from a private spirit of revenge, but from a public spirit for the glory of God, and his justice; and not as a mere imprecation, but as a prophecy of what would be...
And cover not their iniquity, and let not their sin be blotted out from before thee: for they have provoked [thee] to anger before the builders. (e) Let the plagues declare to the world that they set themselves against you and your Church: that he prays only having respect for God's glory and not for any private affection, or grudge.