means,

To Cleanse: specifically, to prune.
In the garden, 'pruning' is a very important activity. There are several reasons for pruning, such as to: correct or repair damage; shape; train; encourage flower and fruit production; create a pleasing form; bring roots and leaves into balance; thin out dense growth to let in light and air; etc. Our Father, the Master Gardener, knows just how, and when, all of His 'branches' need pruning.

I am the true vine, and my Father is the husbandman. Every branch in me that beareth not fruit he taketh away: and every branch that beareth fruit, he purgeth it, that it may bring forth more fruit.
John 15:1-2