St. Bernard wrote about Love

Ave Maria Meditations

Love is sufficient of itself, it gives pleasure by itself and because of itself. It is its own merit, its own reward. Love looks for no cause outside itself, no effect beyond itself. Its profit lies in its practice. I love because I love, I love that I may love. Love is a great thing so long as it continually returns to its fountainhead, flows back to its source, always drawing from there the water which constantly replenishes it.

Of all the movements, sensations and feelings of the soul, love is the only one in which the creature can respond to the Creator and make some sort of similar return however unequal though it be. For when God loves, all He desires is to be loved in return; the sole purpose of His love is to be loved, in the knowledge that those who love Him are made happy by their love of Him.

St. Bernard of Clairvaux