'I Will Repay' in the Bible

And I will strike her children dead [or, "kill her children by some terrible calamity" See Ex. 5:3 LXX]. Then all the churches will know that I am the One who searches the inmost being of people [Note: The Greek says, "searches the kidneys and hearts." In that day these internal organs stood for the inner thoughts, emotions, etc.]. And I will repay each one of you people according to what you have done.