From the blood of Abel
"Righteous Abel", as in ( Matthew 23:35 ) and so read the Arabic version here, and two manuscripts in the Bodleian library, and three of Stephens's copies; the Persic version renders it, "innocent Abel": he is mentioned because he was the first man that was slain, and he was slain because of his righteousness.
Unto the blood of Zacharias;
in the Cambridge copy of Beza's, it is added, "the son of Barachias", as in ( Matthew 23:35 ) and so the Arabic version, "the son of Barasciah"; who he was, (See Gill on Matthew 23:35)
which perished between the altar and the temple;
or "the house", that is, the holy place: and the Ethiopic version renders it, "the holy house"; here he died, being slain by the Jews; see the note, as before.
Verily I say unto you, it shall be required of this generation;
as it was at the time of the destruction of Jerusalem.