I'm an atheist and the absolute zero of spirituality, but I understand what it is to know and not just believe with all my heart that God is real.

I was raised Christian, and for the first third of my life I took it to heart. My family went to church and sent me to a Catholic school, but out of that there was never any saying of grace at meals, calls to pray before bed or any other time, nor were there isolationist comments made about the religious character of friends or anyone else. In short, observant, but mellow. Actually, as a Catholic, they were lucky to even get the observant part of us.

Anyway, I took it seriously on my own, well above what was asked or demanded of me from my parents or teachers. I prayed by myself at night in bed, and I remember well the physical and emotional feelings that washed over me in times of communion. I remember the distinction between belief, and what I had, which was certain knowledge. This is one thing that I think many atheists that have never been very religious struggle with grasping:

They see faith in others as a manifestation of belief. They say "even the word faith implies belief in absence of proof."

Like that matters.

What they don't realize is that to us, faith represented knowledge that was actually stronger and more self evident than a collection of empirical evidence. It was quite simply truer than the Sun always rising in the East.

It's why I don't argue with theists unless we both realize that neither of us is actually trying to convince the other of anything (in that case, let's shoot the shit if I've got nothing better to do).

I'm lucky that I've always been curious and introspective. My faith couldn't survive me looking directly at it in an uncompromising way (my purposeful quest to understand the incredible deepness of my faith is what led to its destruction).

So that was it. That was the last time I felt most spiritual. Somewhere around 15 years of age I'd say. It wasn't anything positive or particularly destructive. Just very intense and misinformed, though there is something to be said for knowing that the omnipotent creator of the Universe personally wants you to succeed. I think the placebo effect is serving a lot of people out there very well.