I thought this was truly beautiful. I don't know why you chose to use 17th century English but perhaps it's to give it that "authentic" nuance so often closely related with the religious dogma of King James. At any rate, I think you could just as well have used modern English and perhaps even more effectively. The measure of a prayer, after all, is not in the pretext but in the content and context. And this has all the finer points of sincerity. It has praise with humility and supplication. I'd venture the only thing it may lack might be thankfulness...and by that, I mean a true spirit of joy in forgiveness and salvation. A true believer never mourns for those we've lost...we mourn for ourselves that we are without them but we celebrate the fact that they are with the Lord. These might be points to consider or not. I still found it a worthy and contrite bit of prayer. I believe every prayer is a poem and every poem, at its best, is a form of prayer. Bless.
A prayer turned well into a profound poem that almost had this secular being want to fully practice the religion that makes up half of his soul. Well done!
Hopefully a better person than I used to be.
I don't write nearly as often as I should, but I'll try to post when I can.
UPDATE: A lot of this writing is now outdated. Proceed at your own risk.. more..