From the blood of Abel, &c. Not that the Jews, to whom Christ spoke, should be punished for crimes which they themselves did not commit nor be more severely punished than they themselves deserved; but he speaks of the Jewish people which, by putting to death their Messias, should shortly fill up the number of their sins; so that God would destroy their whole nation, as if the blood of Abel, and of the prophets unjustly murdered came upon them at once. See Maldonatus.

Of Zacharias, the son of Barachias.[2] Some think this was Zachary, numbered among the lesser prophets, whose father’s name was Barachias; but we do not read of his being murdered in this manner. The more common opinion is, that here is meant Zachary, who, preaching to the people, (2 Paralipomenon xxiv. 20,) was stoned to death in the very place where Christ was now speaking. But there he is called the son of Joiada, and not of Barachias. Some conjecture his father might have had both names; and St. Jerome tells us, that in an ancient copy of St. Matthew, called the Gospel of the Nazarenes, he found this Zacharias, of whom our Saviour speaks, called the son of Joiada. (Witham)

St. Jerome gives another reason why he might have been called the son of Barachias, and not the son of Joiada, and this is to commend the sanctity of the father; for Barachias is interpreted the blessed of the Lord. Others suppose that he was the 11th of the 12 prophets; but it is not mentioned that he was slain between the temple and the altar. Some surmise that it was the father of the Baptist, collecting from the apocryphal writings that he was killed for preaching the arrival of the Redeemer: but that he was the son of Joiada, otherwise called Barachias, is the common opinion. (St. Jerome)

That upon you may come, &c. Not that they should suffer more than their own sins richly deserved; but that the justice of God should now fall upon them with such a final vengeance once for all, as might comprise all the different kinds of judgments and punishments, that had at any time before been inflicted for the shedding of just blood. (Challoner)