[3:73] And do not believe except in one who follows your religion'...
This may refer to the beginning of a command from God (s) to the Muslims. The allusion in it is that you should not associate on intimate terms with opponents, nor divulge your secrets to outsiders.
[3:73 cont'd] ...Say: 'Surely bounty is in God's Hand...
He is the One who singles out whom He will for the lights of instruction and singles out whom He will for abandonment and deprivation.