Symbolism, Imagery, Allegory
Oh man, are swords important, not only because about 99% of the Song of Roland is about fighting, but also because these babies are extensions of their owners' personalities—their awesomeness in fighting, their devotion to God, and yes, even their manliness (how's that for innuendo?).
The swords even have names that express their personalities and the joys of war: Roland's is Durendal (probably from the French "durer," "to endure); Oliver's is Harteclere ("high and pure"); and Charlemagne's is Joyeuse ("joyful"). These are cherished objects, almost like pets. It's no coincidence that in addition to being celebrated for their strength in battle, they are also treasured for their trueness—they are as loyal as dogs.
Oliver, Roland, and Charlemagne are all rad fighters, but at least part of their victories has to be attributed to their swords. In the heat of Roncevaux, Roland shouts to Oliver to draw his sword, for Pete's sake, and quit bumbling around with a shattered spear:
"I have no use for a stick in a battle like this,
Iron and steel must prevail.
Where is your sword that is called Halteclere?
Its hilt is made of gold and its pommel of crystal." (107.1361-64)
It's not just that it's dangerous to fight Saracens who have swords with a chewed-off wooden stick; Oliver's sword itself will bring something to the fight. It's renowned, with its own history of victory. So are Joyeuse and Durendal.
During the fight and his death scene, Roland frequently recalls how many victories he owes to Durendal's swiftness and sharpness (172). This is also why it's such a tragedy to think of your sword falling into the hands of the pagans. It's a dishonor to the sword for all its fine work conquering infidels and spreading Christianity. As Roland dramatically puts it,
"I would rather die than have it remain with the pagans.
God, our Father, do not let France be dishonored in this way!" (172.2336-37)
This is when the swords get even weirder. Just when you thought dog-swords with names were the pinnacle of weirdness, you get Roland's dying soliloquy. He's trying to break his sword so it won't be taken by Saracens but the sword is so good and Christian and true that it just won't break. Whenever he smacks it on to the rock, it rebounds towards heaven. The sword is freaking immortal, an angel of swords. Unlike Roland, it cannot die (173).