Albert Barnes Commentary Malachi 2:8

"But ye are turned aside out of the way; ye have caused many to stumble in the law; ye have corrupted the covenant of Levi, saith Jehovah of hosts." — Malachi 2:8 (ASV)

But you—have departed from the way “of knowledge, truth, equity, fear of God, which I appointed to Aaron and the Levites.” “You have caused many to stumble at the law.” He does not simply say, “in the law,” but “at” it. The law was what they stumbled at. Not only did they misunderstand the law through the false teaching of the priests, thinking it permitted what were truly sins (though this was also true); the law itself was their source of stumbling.

As Jesus Himself was “a rock of offence” on which they stumbled, because through His divine holiness He was not what they expected Him to be, so conversely the law became an offence to them through the unholiness and inconsistency of the lives and ways of those who taught it; just as we now hear Christianity spoken against because of the inconsistency of Christians. So Paul says to the Jews (Romans 2:24), “The name of God is blasphemed among the Gentiles through you, as it is written;” and, for the sins of Eli’s sons (1 Samuel 2:17, Pococke), “men abhorred the offering of the Lord.”

And have corrupted the covenant of Levi—as it is said in Nehemiah (Nehemiah 13:29), “They have defiled the priesthood, and the covenant of the priesthood and of Levi, that covenant which was life and peace” (Malachi 2:5), and, therefore, forfeited them.