Adam Clarke on Matthew 23:7

To be called of men, Rabbi, Rabbi - רבי רבי, i.e. My teacher! my teacher! The second rabbi is omitted by several excellent MSS., by most of the ancient versions, and by some of the fathers. Griesbach has left it in the text, with the note of doubtfulness.

There are three words used among the Jews as titles of dignity, which they apply to their doctors - Rabh, Rabbi, and Rabban; each of these terms has its particular meaning: rabban implies much more than rabbi, and rabbi much more than rabh.

They may be considered as three degrees of comparison: rabh great, rabbi greater, and rabban greatest. These rabbins were looked up to as infallible oracles in religious matters, and usurped not only the place of the law, but of God himself.