From the blood of Abel unto the blood of Zacharias, which perished between the altar and the temple: verily I say unto you, It shall be required of this generation. From the blood of Abel - See this subject explained at large on Matthew 23:34 (note).
Required - Εκζητηθησεται may be translated either by the word visited or revenged, and the latter word evidently conveys the meaning of our Lord. They are here represented as having this blood among them; and it is intimated that God will come by and by to require it, and to inquire how it was shed, and to punish those who shed it.