Is the multiplication of reward purely a grace from Allah, or are there specific considerations for it?

The ability to perform good deeds and have their reward and recompense multiplied is by the grace and mercy of Allah. A good deed is multiplied from ten-fold to seven hundred-fold, and even more, while an evil deed is only recompensed with its like. This increase in reward is a bounty from Allah, which He bestows upon whom He wills. His will, exalted be He, is bound by wisdom, so good deeds are multiplied according to the completeness of sincerity, the need for the action, the state of the doer, and the time and place of the action.