"Batter My Heart, Three-Personed God" is part of the opening verse of "Holy Sonnet XIV" by English poet John Donne (1572–1631), fourteenth in a series of nineteen sonnets he wrote between 1609 and 1610, a time of particularly difficult personal turmoil.
This sonnet contains metaphors of military conquest that describe the poet's desire to have an unfailing faith and to live a life free of sin. In Donne's age, towns commonly had gates that could be shut up against invaders, who used battering rams (heavy poles) to attempt to break down the protective enclosures. The poet begins by asking the "Three-Personed God" (or Trinity of Father, Son, and Holy Spirit in Christian doctrine) to break past ("batter") the doors of doubt and resistance in his heart and to be "made anew" by forces as strong as those used in a military invasion—to "break, blow, and burn." He wants God to capture his heart and give him unfailing faith.
The verses "I, like a usurped town, to another due / Labor to admit you, but oh, to no end" refers to the spiritual conflict the poet is enduring. He wants desperately to return to God, but he is like a town that has been illegally taken over ("usurped") and owes conflicted allegiance to another ruler—sin.
His sense of reason is held captive, and he is "betrothed" (promised in marriage) to the enemy of the Three-Personed God. He begs to be captured and taken prisoner so that he can be forced to return to the God he loves but from whom he has felt alienated.
The final two lines, a rhyming couplet—"Except you enthrall me never shall be free, / Nor ever chaste except you ravish me"—express a powerful paradox. Only if God enslaves him can he be free of sin, and only if God ravishes him can he be truly chaste.