Have they no knowledge, all the evildoers
who eat up my people as they eat bread,
and do not call upon the LORD? (Ps 14.4)
Implicit in the psalmist's words is a particular conception of human agency. He seems to suggest that a person acts on the basis of what she knows and believes. At the same time, those persons who do what is evil must be acting out of ignorance of the truth. If they only had knowledge, the suggestion seems to be, they would not commit their evils against the people of God.
How does this all work? In the history of philosophy, there has been a debate about the nature of human agency and choice. It centers around this question: is the intellect prior to the will, or is the will prior to the intellect? The camp that opts for the first alternative is called intellectualism, whereas the camp that opts for the latter is called voluntarism.
On the intellectualist scheme, human agency is driven by a search after what is perceived to be good. In other words, people are going to make choices based on what they think is good or desirable, and how they judge it best to acquire those things. If people choose to do what is evil, it is because they are ignorant of what is truly good. They have false ideas about what is good. Thus evil and ignorance are closely connected.
This seems to be the picture of agency implicit in the verse cited above: if these evildoers only had knowledge, they wouldn't commit violence against God's people; but as things stand, they are ignorant of the truth, and so they commit evil for which they will be punished.
From all this, we might infer the following practical lesson: we ought to reflect and examine ourselves, to see if we know the truth or not. The scriptures teach us that it is more blessed to give than to receive: do we really know that, or do we just repeat what we've heard? Can I say that I really know that truth, that it's as clear to me as the truth that I have certain rights, or that I ought not needlessly to harm others? Because of I do not see the truth of that teaching, if I don't experience it as knowledge, it will be hard for me to practice it.
Whatever I might tell myself and others about what I believe, the truth comes out in my actions. Then I will really see what I know, and whether I have the knowledge that makes me into a follower of God or not.