Mat 23:8 But do not let yourself be called Rabbi: for one is your Master, [even] Christ; and all your are brethren.

Christ really didn't like the idea of one person following another as the basis of a social order. He was the first egalitarian, preaching that all people were equal and should behave that way. This was revolutionary in his time, but the idea of "following a Master" has a great gravity in every age. People have a strong desire to be followers.

Christ knowing this preached necessary obedience to physical authority, but insisted that they had no moral authority and that we cannot win our knowledge or salvation simply by following a Master. He insisted that every person have a one-to-one relationship with God.

His own status in this regard is cloudy. He says here that he wants us to think of Christ as a brother, that is, an equal, but at the same time, his followers addressed him as "Master" (though not in Matthew) and he doesn't seem to have stopped them.

My sense is that, since he was one with the father, Master was an approapriate title, but as a human being, he wanted to others to see him as a brother. This is why he usually referred to himself as "son of man" rather than as the "son of God."

"Master" is from kathêgêtês, which means "guide" and, by extension, "teacher" and "professor."

"Brethren" is from adelphos, which means "son of the same mother," "kinsman," "colleague," and "brother."