Commentators, generally, have observed that the expression “this generation” of ch. 23:36 refers to the generation of the apostles (see on ch. 23:36). Jesus repeatedly used the expression “this generation” in this sense (see ch. 11:16; cf. chs. 12:39, 41, 42, 45; 16:4; 17:17; etc.; see on ch. 11:16). Obviously, Christ’s predictions concerning the fall of Jerusalem, which occurred in A.D. 70, did, literally, come to pass within the lifetime of many then living.
However, the words “this generation” in v. 34 are in the context of vs. 27-51, which deal exclusively with the coming of the Son of man at the end of the world (see DA 633). The signs mentioned in these verses and in Luke—“signs” in the heavens and “upon the earth” (Luke 21:25)—would take place so near the day of His coming that Christ declared that the “generation” that sees the last of the signs, shall not pass before “all these things [Christ’s coming and the end of the world] be fulfilled.”
Christ did not intend that His followers should know with exactitude when He would return. The signs foretold would testify to the nearness of His coming, but, He declared emphatically, the “day and hour” of that event “knoweth no man” (Matt. 24:36). To make the expression, “this generation,” the basis for reckoning a period of time supposedly terminating with His return violates both the letter and the spirit of His instructions (see on vs. 36, 42).