Mizhdem means accrued consequences. Reward and punishment, although freely used in translations of the Gathas and in common parlance, are not appropriate substitutes for Mizhdem. Ahura Mazda stands beyond revenge and punishment. He is, exclusively, goodness. Asha also guarantees the final victory of righteousness over falsehood that evokes God's omnipotence.
Righteousness is the best of all that is good and is the radiant goal of life on earth.
One must live righteously, and for the sake of righteousness alone. Worldly rewards should not be the motivation. Duty for the sake of duty constitutes selfless service. The realization process of good's triumph over evil is gradual and not abrupt. A dutiful human being, as a co-worker of God, should spread righteousness and eradicate falsehood for the advancement of the world and the progress of man towards perfection.