There are two processes that happen in the washing channels with the beans. The first is called grading the channels where the farmers will rake through the water after pulping. This brings the dense beans to the bottom. These are the ones we want.
Next, they will start washing the channels where they take a grading plank, that looks like a 2x4 board about two feet long and will use the plank to catch the higher grade beans from the bottom, as the less dense beans float right over them.
Just as our beans are washed God wants to wash away all less dense beans and keep the dense ones as we walk in faith with Him.
Psalm 51:2