On The Holy Trinity by St. Augustine
Chapter 10.--There are Three Things in Love, as It Were a Trace of the Trinity.
14. But what is love or charity, which divine Scripture so greatly praises and proclaims, except the love of good? But love is of some one that loves, and with love something is loved. Behold, then, there are three things: he that loves, and that which is loved, and love. What, then, is love, except a certain life which couples or seeks to couple together some two things, namely, him that loves, and that which is loved? And this is so even in outward and carnal loves. But that we may drink in something more pure and clear, let us tread down the flesh and ascend to the mind. What does the mind love in a friend except the mind? There, then, also are three things: he that loves, and that which is loved, and love. It remains to ascend also from hence, and to seek those things which are above, as far as is given to man. But here for a little while let our purpose rest, not that it may think itself to have found already what it seeks; but just as usually the place has first to be found where anything is to be sought, while the thing itself is not yet found, but we have only found already where to look for it; so let it suffice to have said thus much, that we may have, as it were, the hinge of some starting-point, whence to weave the rest of our discourse.