"Selfishness--self-centeredness! That, we think, is the root of our troubles..... So our troubles, we think, are basically of our own making. They arise out of ourselves, and the alcoholic is an extreme example of self-will run riot, though he usually doesn't think so. Above everything, we alcoholics must be rid of this selfishness."
If you believe as I do that selfishness and self centeredness are the root cause of our problems then it makes perfect sense that service work (helping others) which is the antithesis of selfishness is going to help us stay sober. In my view service work (inside AA or elsewhere in the community) is essential to the maintenance of my spiritual condition.