it is the banner of the Arahants and enables them to be devine messengers (the messenger of the path the fourth the Buddha encountered as a Prince before he left the household life).
It also physically embodies the homeless life, making a separation between spiritual seeker and those living the life of the householder.
Blog, Suttas, Aj Chah, Facebook.
He who knows only his own side of the case knows little of that. His reasons may be good, and no one may have been able to refute them.
But if he is equally unable to refute the reasons on the opposite side, if he does not so much as know what they are, he has no ground for preferring either opinion …
He must be able to hear them from persons who actually believe them … he must know them in their most plausible and persuasive form.John Stuart Mill