[Pooya/Ali Commentary 2:270] For giving alms refer to the commentary of verses 261 to 268 of this surah. A nadhr, vow, is a self-directed warning, a reminder of promised action, so that one may be sure of going in the right direction. It is a voluntary undertaking of an act of virtue, binding oneself in gratitude for some special favour prayed for. If one does not constantly give alms and make vows, then one will find his way to loss. The unjust, in this verse, are those who interfere and try to frustrate the undertaking to walk on the right path and block the course of spending in the way of Allah. "Allah knows it" means He accepts both the good deeds and gives reward.