Tafsir of Ar-Ra'd 13:21

والذين يصلون ما أمر الله به أن يوصل

And those who join that which Allah has commanded to be joined, they are good to their relatives and do not sever the bond of kinship. They are also kind to the poor and the needy and generous in nature,

ويخشون ربهم

and fear their Lord, in what they do or do not do of actions and statements. They remember that Allah is watching during all of this and are afraid of His terrifying reckoning in the Hereafter. Therefore, all their affairs are on the straight path and correct, whether they are active or idle, and in all of their affairs, including those that affect others,

ويخافون سوء الحساب

and dread the terrible reckoning