In a system of dress built almost entirely to distinguish offices, the alb is the deliberate exception, and its placement in the sequence of vesting makes an argument.
White, and shared
The alb is a plain white full-length tunic, gathered at the waist with a cord, over which the other Eucharistic vestments are put on; its name is simply the Latin for white. Bishop, priest, deacon, acolyte and lay reader all wear the same alb, and it is explicitly connected to the white garment given at baptism, which every Christian receives.
The order of vesting
A priest vests alb first and then adds the marks of office over it, and the sequence is not accidental. The base garment is the baptismal one, common to all the faithful; the stole and chasuble that distinguish the ordained are put on top of it. The dress therefore states, in the order it is assembled, that ordained office is something added to a Christian identity shared with the whole congregation rather than a separate thing, which is the same claim the theology makes in words.