Near the end of my sophomore year in high school there was a rather irreverent fellow I’ll call Russ, who wrote next to his picture in the Sophomore Section of my yearbook, this phrase:
Na par tho theoulo!
Just as I printed it here. For the record, he was not Greek.
I never did find out what it meant. He died in Vietnam in 1968. 
Before anyone else does it: Google doesn’t know the phrase.
Therefore, neither do I. 
"640K ought to be enou…
oh
Greek phrases. nevermind. carry on.
I know Ancient Greek fairly well, and that doesn’t look like it to me. So maybe it’s Modern Greek, or maybe he had just heard it aloud and was misremembering it? As stands, it cannot be an Ancient Greek phrase. Nai, para to theon would roughly mean “Yes, by god” in Ancient Greek, but that’s not exactly what you have there.
This looks like Liturgical Greek or New Testament Greek. And, from what little I know, it does mean “Yes, by God.”
Brief hijack: Why do so many folks who study NT or Church Greek in the USA but aren’t themselves in a Greek-using Church insist on using the Erasmian (mis)pronunciation?
It is so painful to hear “ha-gee-a so-fee-a” when it is pronounced “a-ya so-fya”. (Of course, that isn’t as bad as when that particular building is called “The Church of Saint Sophia”, when it actually is “The Church of Holy Wisdom”.)
Sorry to resurrect this thread, but I hadn’t seenDogface’s question.
It’s probably because they’ve been taught their Greek by scholars of Ancient (Classical) Greek, where the Erasmian pronunciation is considered correct. It’s a big enough deal for a school to even have Ancient Greek without having two whole kinds. So there’s a differentiation in what you read at later levels but not in the beginning class where you’re taught the basics like pronunciation.