In Luke 22:31-32 we see  Jesus warning to Peter, "And the Lord said, Simon, Simon, behold, Satan has desired to have you, that he may sift you like wheat. But I have prayed for you, that thy faith fail not: and when thou art converted, strengthen thy brother."  What exactly was Jesus talking about? Satan wanted to sift Peter like wheat?  Have you ever heard the saying "To seperate the wheat from the chaff"?  To seperate the wheat from the chaff means to sort out the good stuff from the bad stuff, to know what should be discarded and what should be preserved, to seperate what is usefull or valuable from what is worthless.  Getting the picture here?   It is very important that we keep ourselves close to God.  Satan has no power over us unless we allow it.  One device of satan is to keep you ignorant of God's will for your life.  If he can keep you from knowing God's Word, he can lead you any way he desires.  Satan will use your natural weakness as an entrance into your life.  Whatever your particular weakness is, satan will use it against you.  If he can take us back to our old nature even for a minute, he has succeeded in sifting you.  Chaff is a waste product of grain that is worthless.  It is the dry, scaly casings of grain, a waste material that is usually burned or plowed into the ground.  It has no real worth.  It is only the true wheat that satan seeks to sift.  The precious grain.  We don't hear of satan wanting to sift a Judas.  He dosn't need too.  The Word tells us to be as wise as serpents and as harmless as doves.  As we continue to grow in the Lord and study his word, we are protected from Satans capability to sift us, but we are never free from his desire to do so.  There is a parable in the Word, Matthew 13:24-30 that talks about a farmer who planted wheat, but in the night his enemies came and sowed weeds in his field.  Instead of letting his servants pull them out and take a chance on damaging his wheat crop, he told them to wait until the crops were ready to be harvested, then seperate the weeds from the wheat.  God will always root out the bad seed when the good seed has matured!