In most cases, a "master" in the Bible refers to truth. That can vary according to the person being called master -- Egyptian masters respresent factual, worldly knowledge; when the Lord is referred to as master it means Divine Truth itself. The term does vary according to context. If the things directed by the "master" represent knowledge and ideas, the master will represent desires for good, since desires for good are the things that inspire true thinking.

To be fat and flourishing, as in Psalm 92:15, signifies to be in the goods and in the truths of doctrine. Fat and blood signify interior goods and truths, and hence the Israelites, prior to the Lord's incarnation, were prohibited from eating thereof, because they were only in externals.

Fat signifies celestial life, and blood signifies celestial spiritual life, in Leviticus 3:16.

Fat is predicated of good, and plenteous, of truths, as in Isaiah 30:23.

Fat things, full of marrow, signify goodnesses. Fat and splendid things, as in Revelation 18:15, signify affections of celestial and spiritual goods and truths.

In the opposite sense, in Deuteronomy 32:15, fatness signifies people who are nauseated by good, and despise and reject it because of its abundance. (Apocalypse Revealed 782)

(Referencat: Arcana Coelestia 350, Arcana Coelestia 354)