unfortunately, this excerpt of tagore's insight does not include how he arrived at it, and with time increasing distance to him, one could even suspect he only repeats an appeal to morals and ethics by adding another voice to universal truth.
it seems, to me, all our relations provide only teachers and detachment.
and, as a probably unrecognized side-effect, a prolonged and increased heartache: after all, these teachers did not drive their audiences into total and absolute non-existence.
teaching 1 is morality (Karma) teaching 2 is non-attachment without losing realizations. Teaching 3 is paragate which is self and all realization. With this realization, self and other become more like self and more self. Then suffering has been conquested ultimately, but understood to be part of the games the mind plays, in order explore itself... as was quoted of Jesus Christ "These things too shall pass..."
(of course meaning the limited understandings we sometimes take for ultimate realities, but are nonetheless just limited activities of the mind, rather than the mind itself)