That from the nunnery Of thy chaste breast, and quiet mind To war and arms I fly. (2-4)
The speaker describes a very pure form of love, one in which sex plays little to no part; the "breast" are "chaste," and the speaker compares them to a "nunnery," a place associated with the surrender of sexual desire (and the potential for boyfriends and husbands) and the acceptance of a life of religious solitude.
True, a new mistress now I chase, The first foe in the field; (5-6)
The speaker equates Lucasta and his enemy in battle; they are both "mistresses" of his. This equivalence suggests that there is something similar about chasing an enemy and loving a woman. This could either suggest that there is something sentimental about war or something violent about love. Either way, it's not the most flattering comparison.
And with a stronger faith embrace A sword, a horse, a shield. (7-8)
We have to wonder just a little at the fact that the speaker embraces the instruments of war with a "stronger faith" than he shows towards his lover. Is this because at heart he loves battle more, or is that war brings out a "stronger faith" that other aspects of life just can't?
Yet this inconstancy is such, As you too shall adore; (9-10)
The speaker offers a strange paradox here: he claims that Lucasta will "adore" his betrayal, his inability to stay with her. The lines imply, perhaps, that true love is able to endure disappointment and inconstancy, even though we might not expect it to be able to do so.
I could not love thee, Dear, so much, Loved I not honour more. (11-12)
What's with all the negatives here? (As in "could not" and "Loved I not.") Can the speaker not positively describe his love?