Symbolism, Imagery, Allegory
To paraphrase (okay, to totally invert) Freud's famous cigar quote: a sword is never just a sword. File "swords" in the same folder as "rockets," "towers," "oil rigs" and, yes, "cigars." Now label that folder "images so phallic they're basically NSFW."
And dang if there isn't a whole lot of swordplay happening in The Three Musketeers.
Remember the beginning of the novel where, at the Jolly Miller Inn, D’Artagnan attempts to draw his sword and it’s, um really small? This comes, of course, right after he has been embarrassingly beaten by the inn’s servants and his opponent gets away scot-free without deigning to even draw his sword.
Basically, the better the sword, the better the man. To be a really manly dude, you need both a pretty excellent sword and to be skilled at using it. In other words, it's both the size of the wave and the motion of the ocean. Just check out how keen poor Porthos is to get his hands on a really awesome sword:
Some fragments of past splendor appeared here and there upon the walls of this modest lodging; for example, richly embossed, which belonged by its make to the times of Francis I, the hilt of which alone, encrusted with precious stones, might be worth two hundred pistoles, and which, nevertheless, in his moments of greatest distress Athos had never pledged or offered for sale. It had long been an object of ambition for Porthos. Porthos would have given ten years of his life to possess this sword. (6.12)
Ten years of his life, huh? Wow, that's the kind of bargain most people would strike for only the most important things, like honor or sex (or an object that symbolizes the union of the two).
To cross swords with another man is deemed the biggest honor in D’Artagnan’s world—we’ll leave you to puzzle over the symbolic meanings of that one.