حَتَّىٰ نَعْلَمَ الْمُجَاهِدِينَ مِنكُمْ (...until We know those of you who carry out Jihad,... - 47:31) Allah's knowledge of every person’ s works and deeds is all-encompassing and eternal. It may be noted here that knowledge is of two kinds: [ i ] a priori knowledge or fore-knowledge, knowledge about a thing before its occurrence; and [ ii ] a posteriori knowledge or –in Mariam knowledge, knowledge about a thing after it has actually happened. Here knowledge refers to the second category. Allah’ s knowledge of things is since eternity. In this context, the knowledge about things is a posterioi, after the occurrence of the events in the external world. (ibn kathir) (The purport of this part of the verse is that Allah has enjoined fighting on the believers so that sincere believers may become distinguished from the hypocrites who shrink in horror at the very thought of fighting). Allah knows best.