There is no faith except with a good deed, and the movement of life must be in harmony with the method of faith. Otherwise, If the movement of life separates from the method of faith then it is not called a faith.

الصَّالِحَاتِ (righteous deeds): refers to straight behavior according to the method, the opposite of corruption.

 {فَاسْتَقِمْ كَمَا أُمِرْتَ}

(So remain on a right course as you have been commanded) (Hud: 112)

That is, those who believe and do righteous deeds will have undiminished endless reward, for Allah (swt) will give them this non-decreased reward permanently. It is a reward that is not subject to calculation.

They have done these good deeds in this life as an expression of faith, so the reward will be as described because Allah (swt) has promised of it.