What alliance is the Arcanum 19 referring to?

Answers from the books of Samael Aun Weor

This Arcanum, number 19, is the Arcanum of the Alliance. It represents the “Creator Fire”, the Philosophical Stone.

In order to realize the work which is the Great Work, we have to work with the Philosophical Stone.

Samael Aun Weor. Tarot and Kabala