Mark 1:2

Even as it is written in Isaiah the prophet, Behold. I send my messenger before thy face, Who shalt prepare thy way; The voice of one crying in the wilderness, Make ye ready the way of the Lord, Make his paths straight.

Some critics really have a problem with this passage, because Mark included with his quotation from Isaiah a passage from Malachi, and put it first at that! In fairness to Mark, it should be noted that he did not declare that Isaiah was the author of both passages, his only reason for mentioning Isaiah having apparently been for the purpose of identifying the quotation as Scriptural, which of course it is. One can only be amused at what a passage of this kind does to some critics, all of whom are dramatically reminded by such a passage that the sacred authors were untroubled by many of the punctilious rules so much respected and slavishly followed by themselves.

The passage from Isaiah is Isaiah 40:3, a great prophecy which included in its many implications the prophecy in Malachi 3:1. As Bickersteth said:

The oracle of Malachi is, in fact, contained in the oracle of Isaiah; for what Malachi predicted, the same had Isaiah more clearly and concisely predicted in other words. And this is the reason why Mark here, and other evangelists elsewhere, when they cite two prophets, and two or more sentences from different places in the same connection, cite them as one and the same testimony.[1]

The quotation from the Old Testament emphasizes the divine nature of the ministry of John the Baptist, the heavenly designate who went before the Lord to prepare Israel to recognize and receive the Messiah. The persistence of Israel even to this day of their expectation of Elijah's coming shows the genuineness of the prophecies, Elijah, of course, being the type of John the Baptist. Israel's mistake in their expectation of a literal return of Elijah was due to their failure to believe the revelation of Zacharias, to the effect that Elijah's return would be accomplished by John the Baptist who would go before the Lord "in the spirit and power of Elijah ... to make ready for the Lord a people prepared for him" (Luke 1:17).