Announce to the cities of Judah: Behold your God! (Isaiah 40:9)There is a section of Isaiah that is one of the highlights of all the Old Testament: a prophecy that describes God himself coming into the world. The Jewish Publication Society has study notes for Isaiah 40:9 and following, beginning with the plain though amazing comment on the accompanying verses: "God's arrival in Jerusalem."
God's arrival in Jerusalem is the climax; the earlier verses of the chapter had seen a build-up to this moment. Earlier verses described the herald bringing "good tidings to Zion". Before that, it was proclaimed that all flesh would see the glory of the LORD. And the beginning of the announcement of God's visit to the world is in these familiar words:
A voice of one calling, "In the desert, prepare the way for the LORD; make straight in the wilderness a highway for our God. Every valley shall be raised up, and every mountain and hill made low." (Isaiah 40:3-4).Here, at the beginning of a prophecy of God's arrival in the world, we find a quote that is familiar from all four of the canonical gospels. Mark chooses this quote to be among the opening words of his gospel:
"a voice of one calling in the desert, prepare the way for the Lord, make straight paths for him." (Mark 1:3)By the accounts we have, Mark was Jewish. When Mark identified John the Baptist with Isaiah's "voice calling in the desert", Mark names John as that herald from Isaiah 40 who was announcing the coming of the LORD. The word "Lord" in Greek may be ambiguous; the word "LORD" in the original of the text being quoted was not ambiguous. It was the holy name of God, not to be casually pronounced, a name reserved for God. When Mark identified "the voice calling in the desert" as John the Baptist, Mark thereby implies that the one John announces is the long-awaited LORD, as God whose arrival was prophesied in that passage of Isaiah which he cited. Mark's interest in John the Baptist was only passing; as author of a book about the life of Jesus, his interest was less in how his readers understood John the Baptist, and more in how they understood Jesus.
Many scholars hold Mark to be the earliest of the gospels written. If that is the case, then we have reason to think that the earliest Christians -- and Jewish Christians at that -- may have believed Jesus of Nazareth to be the LORD prophesied by Isaiah, the LORD whose arrival in Jerusalem was expected.