'Foolish' in the Bible

Because that, when they knew God, they glorified him not as God, neither were thankful; but became vain in their imaginations, and their foolish heart was darkened.

An instructor of the foolish, a teacher of babes, which hast the form of knowledge and of the truth in the law.

But I say, Did not Israel know? First Moses saith, I will provoke you to jealousy by them that are no people, and by a foolish nation I will anger you.