A question on morality

As I understand it, we carry out generous and selfless deeds for the purpose of acquiring positive kamma and/or promoting our spiritual quest. However, this seems like a form of greed, one of the three unwholesome roots (I think that's what it is labeled as, unsure). How can moral acts be qualified as free of greed, when it seems that the motive for morality is ultimately self-gain (greed)?