The opposite of truth is falsity.
Truth is knowledge and falsity is ignorance.
So falsity is that which ain't. In order to build up in man a strong character the Menorgs must have truth to do it with. They must know that which is, not that which ain't. Without truth the mind of man becomes daffy. By and through the senses the Menorgs educate man in the realities of life so that he may obtain knowledge that will enable him to proceed with the greater plans that nature has mapped out for him.