The righteous are the face of the Shechinah
When Rabbi Elazar encounters Rabbi Yosi, Rabbi Yehuda and Rabbi Chiya on the road, he tells them he sees the face of the Shechinah. This, we learn, is because when one sees the righteous or pious they represent Her face since She hides within them.
Here we draw the Light of righteousness into our souls so that our faces shine with the radiance of the Shechinah. Further, would any of us, if we met an Angel on the road, recognize the Holy Spirit in him? Would we even register the Angel's presence, as used to ignoring strangers as we are? The Light of this passage ensures that when we gaze into the faces of strangers or friends or family, we recognize the presence of the Shechinah and the spark of Light that lives within all men. Thus, the goal of "Love thy Neighbor" is readily achieved and we complete our purpose in life.