So, there seems to be a normal way in which people address God and ask him for things, and then there's our speaker's way. The normal approach tends to show respect and humility. An example of this is the Lord's Prayer: "Our Father, which art in Heaven, Hallowed [holy] be thy Name. Thy kingdom come. Thy will be done, On earth as it is in Heaven."
But our speaker appears to refuse this approach. He just tells it straight-up, no-holds-barred. Evidence? He starts with a direct command to God ("Batter my heart"). Some Christians would tell you commanding God to do something (as opposed to asking nicely for it) amounts to sacrilege. There's a sense in the whole poem that the speaker thinks he deserves God's attention, which has been lacking, and the speaker goes on and on, maintaining this sense of entitlement: "Reason your viceroy in me, me should defend" (line 7). Note the two "me's" back to back there, and then that word "should." Everything in this poem is about what the speaker wants and deserves. What's more, instead of confessing to abandoning God in favor of the enemy, the speaker blames it all on "Reason," this personified mental faculty given by God. Realistically, can reason really betray someone? Isn't he just betraying himself, and then trying to pass the buck?
But, somehow, he doesn't come off as a totally arrogant, presumptuous jerk. Instead, we think, the speaker seems like a guy who's tried for a long time to get God's attention in normal ways with no success. Like a middle-schooler with a huge crush on someone for a couple years, the speaker here finally just has to blurt out everything he's been thinking in a very short space of time.
And, that's also why he wants God to treat him so violently – he's gone so long without God's attention that he craves it with incredible intensity. In line 6, we see an interesting moment of lament when he says, "but oh, to no end." Here, the speaker seems pathetic, and his other commands start to look more like passionate begging. In fact, we might actually think of the speaker here as self-consciously theatrical. At the most basic level, this is a man who's anguished by unrequited love.
However, there's a huge problem with that reading. Check out the end of line 11: "break that knot again." Unless we're missing something, or the speaker just needed a rhyme with "fain," we find out here that God has, in the past, helped the speaker remove himself from a relationship with the enemy. It seems like the speaker goes through all of this intense, emotional fuss to get God to reveal his presence more forcefully even though God has already done it for him in the past. Why all the drama? Why make himself sound like "a guy who's tried for a long time to get God's attention in normal ways with no success?"
Perhaps the answer, as we just mentioned, is that the speaker is self-consciously theatrical, being provocative just for the sake of the experience of being highly emotional and provocative. Another possibility is that "again" doesn't actually refer to himself, but to another time when God had to break a knot. Some scholars argue that the "again" is an allusion to the moment in Genesis when God expels Adam and Eve from the Garden of Eden because they follow the Devil's advice.
By this logic, when the speaker says, "Divorce me, untie, or break that knot again," he means "either divorce/untie me from the Devil, or you'll have to break the knot between us, just as you did with Adam." If we run with that theory, we should be able to keep up the theory of the pathetic, desperate lover.