Please do not use this statement to justify a charity of any kind. The author speaks about the level of the Mind. When a musician shares his song with others, it hardly means for him it's lost; the spreading makes it stronger and gives him opportunities he didn't have before. The Course takes this idea and brings it to the level where you will be amazed for sure.

If you share a physical possession, you do divide its ownership. If you share an idea, however, you do not lessen it. All of it is still yours although all of it has been given away. T-5.1.1

A major learning goal this course has set is to reverse your view of giving, so you can receive ... God's gifts will never lessen when they are given away. They but increase thereby. W-105.3

To learn that giving and receiving are the same has special usefulness, because it can be tried so easily and seen as true. W-108.6

All that I give is given to myself. W-126