Say (eipon). Second aorist active imperative instead of the old form eipe. The quotation is from Isa 6:9, Isa 6:10. This very passage is quoted by Jesus (Mat 13:14, Mat 13:15; Mar 4:12; Luk 8:10) in explanation of his use of parables and in Joh 12:40 the very point made by Paul here, “the disbelief of the Jews in Jesus” (Page). See note on Mat 13:14 for discussion of the language used. Here the first time (“go to this people and say”) does not occur in Matthew. It is a solemn dirge of the doom of the Jews for their rejection of the Messiah foreseen so long ago by Isaiah.