THE OFFICE OF TEACHER was described to the apostles by our Lord under the figure of the light of the world. They were, He said, to enlighten the world, which was lying in the darkness of sin and unbelief, by their their teaching and example, thus showing the way to heaven. They being the vanguard of the Church, all eyes would be directed to them. Under the same figure our Lord taught them that they could not give light of themselves, but that He would kindle the light in them. Their light was borrowed light, but they must let this light shine through them in such a way as to make themselves models for the whole world by their words and deeds.
[From 'A Practical Commentary on Holy Scripture' by Bishop Knecht, D.D.]