'Understand' in the Bible

And I will kill her children (followers) with pestilence [thoroughly annihilating them], and all the churches will know [without any doubt] that I am He who searches the minds and hearts [the innermost thoughts, purposes]; and I will give to each one of you [a reward or punishment] according to your deeds.

Because you say, “I am rich, and have prospered and grown wealthy, and have need of nothing,” and you do not know that you are wretched and miserable and poor and blind and naked [without hope and in great need],

His eyes are a flame of fire, and on His head are many royal crowns; and He has a name inscribed [on Him] which no one knows or understands except Himself.