P1) We understand that moral virtue should make us happy, as it is not right that unhappiness is the reward of moral virtue, nor that immorality be rewarded.
P2) By 'ought implies can', if we ought to achieve the summum bonum by living moral and virtuous lives, then we can achieve the summum bonum (it is a real possibility)
P3) The summum bonum is not possible in this life (as Good will would not be the intention of a moral action and phenomenal states cannot be perfect nor universal) as bad things can happen to good people and vise versa.
P4) For the summum bonum to be possible, if not in this life, it must therefore be achievable in another life
C1) Therefore, for moral duty to be a real concept with value, we must therefore be immortal
C2) Only God, an all-powerful morally pure being, could guarantee our immortality and the real possibility of the summum bonum. Thus, the very possibility of morality needs God