How is it a particular curse to be cast out of the presence of God (Gen 4:15)?

First Adam and Eve were cast out of the immediate presence and guardianship of God in the Garden, and then Cain was cast wholly out of his presence. This is just the first of many instances of God’s hiding his face from those who have sinned: “And I will surely hide my face in that day for all the evils which they shall have wrought” (Deut 31:18). The reason this is a curse, of course, is that God provides for and blesses man.