That God is infinite and creatures are finite can be demonstrated both in reason and supported by the Bible.
Anything that has a beginning is finite, for there was a time when it was not, yet now it is. This is the definition of a creature, e.g., a created thing. Thus anything with a beginning point was created by a prior cause and is limited by time. Further, all things created were moved from potential to actual at the point of creation. All things with potential are limited by that potential, since they have the potential to not be created, and the potential to be created with other limitations or perfections, such as size or weight, depending on the act of the agent causing the created being. Further, created beings have the power to change, which is evident by our universal observation of all created things changing. Anything that changes is not infinite, since the change is a gain or loss of form or accident. An infinite being cannot gain or lose, since an infinite cannot be greater or fewer. Therefore anything created is finite, limited by potentiality, and is changing.
God, being uncreated, does not have a time when He was not. God was not caused to come into being by another, and therefore must be the first cause, or there would be an infinite regress, which is absurd. God also does not change in His being, for there would have to be an agent causing this change, which would also result in an infinite regress, which is absurd. Further, God is not made of matter, since all matter is limited by form and individuality, and anything limited is not finite.
Therefore God is uncreated, without beginning, not made of matter, and is the first cause. God is also distinct from all created things, for created things are finite, as demonstrated above. Since there is an infinite difference between the finite and infinite, God cannot be confused with any created thing.
This demonstration is supported by the Bible, which tells us that God is timeless (He is the one who was, and is, and is to come, Rev. 1:8; from everlasting to everlasting Ps.90:2; uncreated (the self-existing one, Ex. 3:14; He created all things that are created, Gen. 1:1, Jer. 32:17; Col. 1:16-17); all powerful and all knowing (His understanding has no limit, Ps. 147:5; Is. 40:28;), and unchanging (Num. 23:19).
Creatures, however, are evil (there is none righteous, not even one, Rom. 3:10-18; none are holy like God, 1 Sam. 2:2;), created (Gen. 1:1;) changing (Luke 3:5;); and subject to corruption (Gen.3:17-18; Rom. 3:23).
Thus God is infinite and all created things are finite, and there is an infinite difference between them.