Threshing separates grain from chaff, so dream books read it as sorting the valuable from the useless. It speaks of discernment and of harvesting what truly matters.
Where in your waking life have you met something like this lately?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.