Adam Clarke on Luke 11:51

From the blood of Abel - See this subject explained at large on Mat 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.