The subject of Donne's Holy Sonnet 14 is religion, even if it's masked by love, sex, and general mayhem. At the most basic level, this is a poem in which a man asks for forgiveness and salvation from God, but he expresses his frustration that God hasn't revealed himself forcefully enough. The speaker, though, is unclear on what the forgiveness and salvation will entail, and how to make sure that God's message gets through to him.
The speaker of Holy Sonnet 14 is more interested in worshipping himself and his own rhetoric than any sort of higher spiritual authority.
Complicating the speaker's desire for salvation is the fact that he loves God in more than just the regular spiritual way. He seems interested in marital and sexual forms of love, as well. The bottom line is that he's unsatisfied with the kind of love where one's relationship with God is one-sided worship. He wants to feel loved back, and he's not sure how God can manifest that love.
The speaker's love for God is an easier, more natural expression for him than his plea for abuse. His language flows much more calmly and easily in the lines of the sonnet where he expresses his love directly.
Sex in this Holy Sonnet 14 is a metaphor our speaker uses for the way in which God might demonstrate his love for the speaker. The speaker really wants a close, reciprocal relationship with God, and one of the only ways he can imagine a relationship like this working is through an encounter of a sexual nature.
While the identity of God breaks down from the first line, the speaker uses the whole sonnet to build consistently toward a sexual, rather than spiritual, resolution.
Violence is a way in which the speaker of Holy Sonnet 14 imagines God manifesting his love. God's more gentle efforts to remind the speaker of his presence haven't done the trick, so the speaker demands more extreme gestures like breaking, blowing, and burning.
The meter and phonetics of the concluding couplet suggest that sex is a gentler and more intimate act than the violent imagery around it would suggest.
Warfare makes up the major extended metaphor of Holy Sonnet 14, as the speaker presents himself as a captured fortress city. He calls upon God to storm the walls and retake the city. What's curious about this metaphor is that, if the speaker is the city and God is the attacker, God is going to have to do some major damage to the speaker in order to save him. Questions of what it means to be an attacker or a victim dovetail with the notions of rape and ravishment in the poem.
Holy Sonnet 14 can be seen as a reworking of the story of Sodom and Gomorrah, as the speaker begs forgiveness to ward off the destruction of the two cities.