The idea of loving Hashem as our “husband” is that we experience a fiery love for Hashem. Just as a wife has a fiery love and desire for her husband, so too our soul has a fiery love and yearning for Hashem’s Infinite Light to shine into us. Through this fiery yearning for Hashem, He does shine His Light into us, so that we can be enveloped in experiencing His Light.
Seemingly, the Alter Rebbe is using the idea of calling Hashem “my fire” in two different meanings: 1- I have a fiery yearning for Him, 2- When He shines His Light upon me it is a truly fiery experience.
In other words, there are two “fires”: There is the fire inside of our soul yearning for Hashem, and there is the fire of G-dliness that comes down into us when we truly yearn for it. (For more about these two “fires” see Likutei Torah Parshas Shlach page 44c.)
So far, the Alter Rebbe explained the idea of ‘רְאוּבֵן-Reuven,’ which is the idea of “seeing” Hashem in prayer. This is done by “gazing at the Glory of the King” through deep contemplation on His greatness and the contrast between that our current state of restraint and concealment on the Divine soul. This “seeing” Hashem in prayer produces a fiery love for Hashem and a yearning to actually experience and be enveloped by His Light.
