I will list a number of things that human reason can view as evidence of God’s infinity.
(a) In the entire created universe, no two things can possibly be the same. It is impossible for any two things to be identical at any given point in time, as human scholarship and reasoning have seen and verified. Yet the substantial and physical things in the universe viewed one by one add up to an infinite number. Neither can the world have two identical situations over time. As you can see from the wobbling of the earth caused by the misalignment of the axis to the poles, the earth never comes back to the same spot. This is also provable from human faces. In the whole world, not one face exists that is the same as another or similar in every way. Nor will there ever be two identical faces to eternity. Infinite variety like this could occur only as the result of God the Creator’s infinity.
(b) No one’s character is completely like another’s. As the saying goes, there are as many opinions as there are people. Therefore no mind, that is, no will and intellect, is the same as another or similar in every way. As a result, no one’s speech is identical to anyone else’s, either in tone or in the thought behind it. Nor does anyone’s action copy another’s to a T, either in manner or in the emotion and inclination behind it. This infinite variety as well is like a mirror in which we can see the infinity of God the Creator.
(c) In all animal sperm and in all plant seeds there is an intrinsic kind of immensity and eternity—immensity because it can be replicated to infinity, and eternity because its replication has continued without interruption from the creation of the world until now and will continue perpetually. As an example from the animal kingdom, take fish in the ocean. If there were as many fish as there are fish sperm, within twenty to fifty years fish would fill the ocean to the point where it contained nothing else, causing the water to flood the whole planet and destroy it. To prevent this, God has provided that fish become food for other fish. The same would happen with plant seeds. If all the seeds that one plant produces each year were planted, within twenty or thirty years they would cover the surface of not just one planet but many. In the case of some bushes, each seed will produce hundreds or even thousands of other seeds [in a year]. Calculate it for yourself, multiplying the production of one such seed twenty or thirty times over, and you will see. The divine immensity and eternity cannot help but be reflected in some way. The two commonly experienced phenomena just discussed make these divine qualities visible.
(d) To an enlightened reason the infinity of God can become apparent from the fact that every academic discipline can grow to an infinite extent. So, therefore, can our intelligence and wisdom. Both intelligence and wisdom are capable of growing from a seed into a tree, and from a tree into forests and gardens of trees—intelligence and wisdom have no end. Our memory is their soil. They germinate in our intellect; they bear fruit in our will. In fact, these two faculties, our intellect and our will, are capable of being cultivated and improved to the end of our lives in this world, and afterward to eternity.
from True Christianity, Volume 1, Section 32