“knowledge.” This is a clear example showing that the Semitic understanding of “knowledge” is different than the Greek (and modern) definition. To the Hebrews, a person did not “know” something if he did not act on the knowledge. To the Hebrews, knowledge and action were conceptually combined. In contrast, the Greeks were much more cerebral, and more carefully separated knowledge from action. A Greek could “know” something but not act.
In this verse, it is not just “knowledge” that delivers the righteous, but the fact that the righteous person will act decisively on what he knows. In this context, the wicked “neighbor” (which in Hebrew includes anyone close by, such as a family member) is saying harmful things, and the righteous person finds out about it and acts to counteract the harm. Note that the righteous person does not “just pray about it.” He would have prayed, but he would have acted in some way as well. Too often the wicked have more effect than they should have because the righteous do not take action.