The gift must disappear

The giver of a gift does not calculate its worth nor does he give for the sake of the return gift. 

Before the recipient can properly reciprocate, the gift has to disappear. In that disappearance lies the autonomy of the gift reciprocator. 

When God gives man His providence without expecting a return He is empowering man in His autonomy. That the return gift is out of the giver's control means, in the case of God as the giver, that man exercises his autonomy most essentially when he appreciates and returns God's gifts.