In offering a greeting, one proclaims the other to be worthy of notice, worthy of some of his space. In refusing to return the greeting the other rejects the commonality of the first, even his humanity...
God’s actions in the world are not only actions, they are gestures to us, and when we understand them as such, we are bidden to respond. For those who see that the heavens are really God’s heavens, the gift of the earth must be responded to.
Whatever its literal meaning, the functional meaning of “Barukh atah” is “You are Present” and the blessing—when said mindfully—helps establish a relationship with God in the phenomenon at hand; in the taste of the apple, the smell of the rosemary. Jewish tradition even demands a blessing on hearing bad news, because God is somehow present even in tragedy, and can (and must) be met there.
...The refusal to respond to a beggar is linked to idolatry because there is no essential difference between erecting a wall against one’s fellow and erecting a wall against God, who demands to be treated as a “subject”, to be looked directly, so to speak, in the face. The experience of another subject creates a demand upon us by its very presence to make room to respond.