I once heard this question posed by a Christian in a debate, in which he tried to demonstrate that his atheist opponent’s very conception of God was faulty, meaning he was arguing against a “smallish” and rationalist idea of God. One of the greatest Western fathers to read devotionally and philosophically on this issue is Anselm of Canterbury. Anselm is probably most famous for his version of the “ontological” argument for God’s existence, where the very idea of God requires that he exists, otherwise one is not thinking of the correct God. This is closely tied into the idea of the “greatest being,” or “that, than which nothing greater can be conceived.” In Anselm’s Prosologion, this thinking is done in prayer, as he tries “imperfectly” and “tainted by sin,” to try and understand more of God’s nature and attributes in order to understand and worship (he quotes the Psalms throughout). A few examples should suffice to demonstrate how we should think about how “big” the Triune God really is.
One of the first ideas of God being the “greatest possible,” is in the area of attributes. Classical Christian theology uses positive terms such good, just, merciful, beautiful, etc…and ascribes them to God “to the max (or infinite).” However, one must be careful to not make the attribute greater than or equal to God, because that would mean God is less than or equal to that concept. In other words, it is wrong to say “God has justice,” but completely proper to say “God is justice.” Put another way, the very idea of what we view as universal virtues and goods are a reflection of the divine nature, who is these attributes by nature.
The same idea applies to the natural world. If time, matter, or any part of creation is believed to have existed before or at least always with God, this means it is either greater than or equal to God. This is incorrect, and is one of the reasons (there are several) the church (and many Jewish traditions) have God creating the universe ex nihilo (out of nothing). This means God is outside of time, even when he chooses to act within time (such as the incarnation). Many debates both within and outside of Christianity often forget this idea.
Finally, Anselm posits that the very idea that the God of the Bible exists is better than him not existing. Since it is better to be alive than dead, or to exist rather than not to exist, God must exist, otherwise “your God is too small.” In order for him to be the greatest being, he must exist, otherwise he is not the greatest being. One might have to read this a few times in order to completely “get” this argument, but if you ponder the first few “greatest” ideas it will start to make sense. Remember, this argument only works for the “greatest possible” being, of which there can only be one. So arguing that this can prove Santa Claus or Atlantis means you’ve missed the point (a mistake Anselm’s critics made even in his day).
In a climate that emphasizes immediacy and efficiency, such contemplation of God is often deeply unpopular or considered “irrelevant” or “impractical.” For this reason (and many more) I highly recommend reading Anselm and other church fathers, since they are “anti-trendiness with a vengeance.” Even if one disagrees with what’s read, it forces a 21st century post-Christian culture to “think differently.” Thinking about such greatness makes our ever increasing list of invented psychological problems seem rather trivial and unimportant by comparison. The Triune God truly is “that, than which nothing greater can be conceived,” and we owe him his due.