“Separate that spiritous earth from the dense or crude by means of [engaging in the sexual act, entering the flames, with love for your spouse and serene, stable awareness, to gradually transform the flames into] a gentle heat with much attention [patience, and forbearance].”
If the flame is hot, do not stay long within it or you will be burned. Yet do not avoid entering the furnace, either!
You have an embryo of a soul within and this can love. Indeed, this is an embryonic love because it is an embryo of Soul; yet if you annihilate [the flames of] desire you will feel that spark of love. When you learn how to feel that spark, then that spark will become a [pure] flame and you will experience [the reality of] that which is called love. Therefore, strengthen your embryo of soul with the blessed flame of love [through sexual magic], and then you will achieve the miracle of your incarnation. It is necessary for you to be integral and that is only possible by loving.
In the Nineteenth Arcanum, a great Alliance is established between two souls. Man and woman must kill desire [through purifying the sexual act] in order to achieve the great Alliance. If you want to incarnate your soul, you must then celebrate the great [sexual] Alliance of the Nineteenth Arcanum. - Alchemy and Kabbalah in the Tarot