3. All therefore--that is, all which, as sitting in that seat and teaching out of that law.
      they bid you observe, that observe and do--The word "therefore" is thus, it will be seen, of great importance, as limiting those injunctions which He would have them obey to what they fetched from the law itself. In requiring implicit obedience to such injunctions, He would have them to recognize the authority with which they taught over and above the obligations of the law itself--an important principle truly; but He who denounced the traditions of such teachers (Mt 15:3) cannot have meant here to throw His shield over these. It is remarked by WEBSTER and WILKINSON that the warning to beware of the scribes is given by Mark and Luke (Mr 12:38; Lu 20:46) without any qualification: the charge to respect and obey them being reported by Matthew alone, indicating for whom this Gospel was especially written, and the writer's desire to conciliate the Jews.

JFB.