Batter my heart, three-person'd God; for you As yet but knock, breathe, shine, and seek to mend;
The speaker begins by asking God (along with Jesus and the Holy Ghost; together, they make up the "three-personed God") to attack his heart as if it were the gates of a fortress town.
If you are caught up on the word "batter," note that back in medieval times, in order to break down the door of a fortress or castle, you'd have to use a battering ram. It's a huge pole of wood, possibly with a ram carving on the front.
He asks God to "batter" his heart, as opposed to what God has been doing so far: just knocking, breathing, shining, and trying to help the speaker heal.
Those actions are nice and all, but Donne wants something a little more intense. Scholars focus a lot on these verbs, and the words are certainly stressed in the line (notice how you accent these verbs and pause between them when you read the poem out loud), so let's break them down a bit.
First of all, none of the verbs are particularly active. God asks to come in by knocking, which is nice, but he also just breathes and shines, two things that he might do out of necessity — not choice. When we breathe, it's normally not because we choose to, and the same applies to things that shine.
The "mending" seems nice, but note that Donne says "seek to mend," and not just "mend." Does God really "seek to" do anything? Doesn't He just do it, if he's all-powerful?
So, what about the specific actions? Are they particularly significant? Well lots of scholars think that the three verbs mirror the set-up of a "three-personed God" (the Christian notion of the Trinity). Thus, they associate the Father with power as he knocks but ought to break, the Holy Ghost with breath as he breathes but ought to blow like a strong wind, and the Son with light as he shines but ought to burn like fire.
These actions make some sense as representative actions of each part of God, but other scholars argue that, based on the Bible, it isn't clear which member of the Trinity should be understood to do which of the actions. The confusion about which aspect of God does what appears to be purposeful.
If the speaker wants to make things easier, he can very well put the verbs in the traditional order in which the Father, the Son, and the Holy Ghost are normally described.
But, the Trinity isn't the only way to read those verbs. Some scholars point out that these terms (especially when combined with the other series of three verbs in line 4) all make sense in the context of metal- or glass-blowing (the process of shaping glass and metal objects). In this way, scholars see the speaker as making God into a craftsman who can, like a glassblower, "blow" life into the object (the speaker).
That I may rise, and stand, o'erthrow me, and bend Your force, to break, blow, burn, and make me new.
Lines 3-4 continue much like lines 1-2, with the speaker asking God to treat him violently.
He asks God to "bend your force," which may mean to "make use of your power."
More importantly, even though it takes him four full lines, the speaker finally gets to the point of why he's telling God to do all this. His goal, as he puts it, is to "rise" and "stand" and become "new."
This can work in two ways. First, there's the born-again angle, where the speaker asks to have a moment of religious epiphany. He wants to recognize God's power, but he worries that the only way God will get through to him is by doing something violent and completely overthrowing his life.
On the other hand, "make me new" is probably a reference to the Christian idea that true happiness and salvation come only after death, and that, in order to get into Heaven, earthly life must be a continual act of suffering. That may be why our speaker wants to be abused and broken in the earthly world — so that he will be worthy for the afterlife.
A quick note on the language here: read these lines aloud, and notice how the word "o'erthrow" makes you take a big pause and change the rhythm of your speaking, and how violent and intense those alliterated b-words are ("break, blow, burn"). These words get a lot of attention verbally, and it's a cool example of words' sounds reflecting their meaning. Onomatopoeia anyone?
I, like an usurp'd town, to another due, Labour to admit you, but O, to no end.
Here comes the explanation of that whole "battering" business. The speaker compares himself to a town that is captured or "usurped."
The phrase "to another due" suggests that the town belongs to someone else, but it's tricky because we don't know who this "someone" could be.
Whose was it originally, and who took over? The likely possibility is that it was originally God's, and it was subsequently taken over by another, but that doesn't help us figure out who the "other" is.
In any case, the speaker wants to let God in, but he's unsuccessful so far.
These lines are interesting in part because, unlike anywhere else in the rest of the poem, Donne actually uses a simile here instead of a metaphor. Instead of saying, "I am a usurped town," he leaves more room between himself and the town by only saying that they're similar.
What's the big deal? Well, it suggests that the speaker is conscious of how unrealistic his requests are. Where, in the first few lines he directs God to overthrow, break, blow, and burn him, it's not until this line that we know he's being metaphorical (instead of actually wanting to be broken, burned, and so forth).
The "oh" in line 6 is another linguistic choice worth mentioning. There are two ways we might see this:
First, we can read it as the only moment of truly honest self-expression in the poem, where the speaker lets his words go without careful control. In other words, the "oh" is the only word in the poem that isn't actually a word – it's more of a sound, a sigh, or an exclamation. It's a different kind of language, and one we don't see elsewhere in the poem.
If we read it as a sigh, it might lend this line some extra emotional pull if he seems sad that he can't let God in.
On the other hand, you might think the "oh" is theatrical and overly dramatic, like a "woe-is-me!" moment.