I was raised Catholic, by a deacon, and have a deep understanding of Judeo-Christian religions, and have studied to a lesser extent several world religions. What am I missing?
That is natural, but the problem is that our intellect is quite limited. You would like to have a description of "the unifying deep truth". But even very simple experience, like how strawberry tastes like, cannot be transmitted by words and comprehended by the intellect. How could we transmit something vastly more complex even if we knew it -- and I am not claiming I do.
So I would say what you are missing is the direct experience of something higher. Seek and you will find.
Spirituality does not contradict with what others experience in material world.
You just start identifying more with consciousness and less with the body. That's the shift.
And if you also think about it scientifically it makes sense.
You are consciousness experiencing the world.
Not the body experiencing consciousness.
You are consciousness
Not the body.
The body ages. The cells changes. You remains. The consciousness sees the body.