in 3x01 dean is singled out and attacked by the demonic embodiment of lust, and tamara is attacked by wrath. considering that the demons themselves assessed tamara's personal vice to be wrath, this also draws a connection between dean's assailant and his threesome at the beginning of this episode—aka, the episode is suggesting that dean's vice is lust. but what these two assignments do is set sam up for something more interesting.
sam is attacked by three of the demons: pride, gluttony, and greed. if dean and tamara are attacked by the manifestations of their own vices, then the episode is implying that sam is as well. with pride as the clear leader of the trio, it reasons that pride is sam's greatest vice. this, i believe, can speak to his characterization across seasons 1 and 2. with gluttony and greed standing silent in the background though, there's perhaps an element of foreshadowing.
pride himself gives sam his title "boy king." that draws a clear line between these vices and sam's fate, and therefore the foreshadowing can be realized in his demon blood addiction, which is frequently throughout season 4 referred to as a hunger for power. so gluttony and greed loom in the background of sam's life, promising that he will succumb to those vices inevitably for as long as he continues down the path of fate.
and then ruby, the very embodiment of that fate, appears out of nowhere to save sam from them, seemingly killing all three of the demons. and then she proceeds to throughout seasons 3 and 4 nurture those vices, sweetly coaxing them out and encouraging him down that path. she "saved" him by leading him down the very path he thought he was avoiding. and this is parallel to all the other ways ruby manipulates him: she draws him closer to fate while pretending to push him away—see for example the way she embodies dean, the opposite of fate, and uses that mimicry to pull him toward lucifer. therefore 3x01 serves as foreshadowing for sam's narrative arc throughout the next two seasons as he falls prey to his own dormant vices and ruby covertly nurtures them until they consume him whole.
