Natural love exists in the angels, for to every nature there belongs an inclination which is called natural appetite or love. This inclination exists differently in different natures, according to the mode of their being. In intellectual natures it exists according to will; in sensitive natures according to sensitive appetite; and in natures without understanding only in a bias which belongs to the order of nature; as explained above.
In the angels this natural love differs from elective love; for the former regards the good which is desired as an end, and is called natural dilection; while the latter is derived from the former and regards the good which is desired for the sake of the end. Thus both angels and men desire their own good and perfection, and choose some good by election.
Beings love each other by natural love where they agree in nature. In so far as they agree or differ from anything else it does not belong to natural love, which signifies only that tendency which is found in everything towards what is of the same nature with itself (as we see in inanimate things, e.g. fire, which has a natural disposition to communicate its form, which is its good): so that in so far as the angels love what differs from themselves it is not by natural love.
Angels and all creatures love God more than themselves, because God is the Universal Good, and it is natural to everything, in so far as it belongs to anything else, to be more inclined to that to which it belongs than to itself. Thus a member will naturally expose itself for the preservation of the whole body; and as reason imitates nature, we see also in politics that a good citizen will expose himself to danger for the preservation of the city.
- text taken from Compendium of the Summa Theologica of Saint Thomas Aquinas, by Bishop Berardus Bongiovanni