What do the ancients mean by calling people masters in fortune-telling books?

Refers to monks who are strict in discipline and proficient in Buddhism.

A man of virtue is a respectful name of a monk, because he has the connotation of virtue and wisdom, and he is superior to others outside.

And:

1. Used as honorifics for elders and monks in ancient Chinese.

2. In some local languages, the owner refers to the elder in the family.