In ancient Israel the process of sifting the wheat was the last stage in preparing the harvest. The sifting occurred once the wheat had been gathered in and winnowed (tossed in the air to remove the chaff). The wheat was gathered up off the floor or ground and shaken in a sieve to remove the rocks, dirt and other debris that may have been gathered in with the kernels of wheat.
When the Lord tells his disciples that Satan desires to sift them as wheat, they have already been identified as "wheat." They are not the chaff that has been blown away in the whirlwind, a term used by the Lord to describe the condition of those who are disobedient and do not hearken to the voice of the prophets.
Sifting occurs later. The wheat is shaken and falls to the ground and what is left in the sieve is rubble, dirt and trash. I would assume that the sifting process, according to how we respond to it, can either purify us that we may be gathered into the garner cleansed from the rubble of the natural man, or we lose our faith and the debris of the world is what remains with us. Peter was sifted and came out stronger for it. He triumphed over Satan. We will each be "sifted." We will each decide the end result of that sifting.
My purpose for blogging is to have a place to explore a few thoughts with family and friends and whoever else may drop by. Feel free to make comments whoever you are. I have another blog entitle This I Know that is an exploration in spiritual thought at www.hopeallthings2.blogspot.com