In biblical text, threshing wheat was a way to separate the good parts from the bad parts (remove the wheat from the chaff). In Luke's gospel, Jesus tells Simon (Peter) that Satan has asked to have him and sift him like wheat. Meaning, he wants to separate him from what's good in Him and what's good for him. But Jesus prayed for him, that his faith would not fail. Jesus is interceding on your behalf, Don't Give Up!