5. Nothing else moves God to the production of creatures but His own goodness, which He has wished to communicate to other beings according to the manner of their assimilation to Himself (B. I, Chap. LXXXVII). Now the likeness of one thing may be found in another in two ways: in one way in point of natural being, as the likeness of heat is found in the body heated; in another way in point of knowledge, as the likeness of fire (perceived) is in sight or touch. In order then that the likeness of God might be in creatures in such modes as were possible, it was necessary that the divine goodness should be communicated to creatures, not only by likeness in being, but also by likeness in knowing. But mind alone can know the divine goodness. Therefore there needed to be intelligent creatures.
6. In all comely arrangements of things, the attitude of the secondary to the last imitates the attitude of the first to all, as well secondary as last, though the imitation is not always perfect. Now God comprehends in Himself all creatures (B. I, Chapp. XXV, LI, LIV); and this is represented in material creatures, although in another way: for the higher body comprehends and contains the lower, according to quantitative extension;* whereas God contains all creatures in simple mode, and not by quantitative extension. In order then that an imitation of God might not be wanting to creatures even in this mode of containing, there were made intellectual creatures to contain material creatures, not by any extension of quantity, but simply by mode of intelligence: for what is understood is in the mind that understands it, and is comprehended in its intellectual activity.
2.45 : The real Prime Cause of the Variety of Creatures
2.47 : That Subsistent Intelligences are Voluntary Agents