General Book of the Tarot, by A. E. Thierens, [1930], at sacred-texts.com
". . . the Genius of the Sun holding two cups and pouring from the one into the other the liquor which holds life." (P.)--" A winged angel with the sign of the sun upon his forehead . . . pouring the essences of life from chalice to chalice." (W.) Another version has: ". . . pours the fluid of Life from a
golden vase into a silver one." (P.) This is evidently the cosmic function next to the Sun, messenger of the same: Mercury or Vulcan, lord of the sphere of Virgo, surrounding the solar Leo-sphere. Other traditional descriptions confirm this: "It is the symbol of combinations, working incessantly in all regions of Nature." (P.) On his breast this angel bears a square with inscribed triangle, reminding us of the passage of the cosmological Stanzas of Dzyan, "The Three fall into the Four," which means the beginning of Manifestation. "Entry of Spirit into Matter and reaction of Matter upon Spirit." (P.) So on the subject of this card there seems to be perfect understanding. "Incarnation of Life," P. adds. This is Mercury, who has to do with the distribution of life-currents from the Sun farther on into the solar-system and from the heart and solar-plexus farther on into our physical body. The golden vase and the silver one illustrate this distribution from higher to lower regions.
So this card signifies all sorts of distribution, from the nervous system and its workings of co-ordination to correspondence by the post office, letters and communications, and the latter not only limited to this physical world but extended to other planes of existence. The function of Mercury is that of the mind in its concrete activities and imparts knowledge, learning, which after all is the beginning or potentiality of all our further relations in this world.
P. seeks to establish relation between it and the Hebrew letter Nun, which means "the offspring of the female--(we said rightly, that Mercury has much to do with the Moon)--a son, the fruit of any kind . . . the image of the being produced or reflected. . ."
[paragraph continues] Yes: reflection and above all reproduction. The name 'Temperance' appears to have been chosen because of the transposition from one plane to another, or one centre to another, which has much to do with 'time' also. The latter is the proper reason for naming this principle directly after that of Saturn.