Separating the Wheat from the Chaff:

"He will throughly purge his floor, and gather his wheat into the garner; but he will burn up the chaff with unquenchable fire." 

 Matthew 3:12

While living in Korea, I observed often the grains of rice being separated from the chaff. The rice, husks and all, would be piled onto a smooth surface. The process required a windy day to be beneficial. The grains were thrown up into the air with a device called, in the Latin, a tribulatim. The wind would carry the husks away and the pure grains would fall back to the earth. 

I compare this process to the work of the Holy Spirit in separating the elect of God from the chaff of the world. Tribulation is often the tool, and the Winds of the Holy Spirit the means, by which God discerns the difference between the two.