“My puny little brain can’t really grasp the concept because I can’t really grasp the concept of infinite God. Omnipresence is too much for me to mentally grasp.”
The infinite God didn’t come up with the concept of the trinity, people did. (Trinity isn’t even mentioned in the bible) people who are as imperfect and finite as you and I. If these men who made it all up can understand this concept, omnipresence obviously isn’t necessary to understand it.
Why is it that even today, Jews (and you can hardly call them christians) still say, “Our God is one God”?
My guess would be that they don’t see Jesus or the Holy Spirit as equal to God.