What is the meaning of [Brag is a good dog, but holdfast is better]

A variation of “Talk is cheap”,”This Proverb is a Taunt upon Braggadoccio’s, who talk big, boast, and rattle,It is also a Memento for such who make plentiful promises to do well for the future but are suspected to want Constancy and Resolution to make them good.” – Divers Proverbs, Nathan Bailey, 1721. 4