The answer is: Isaiah

Isa 40:3

In the Gospel of Mark, we kick off with a stunning introduction that not only captures our attention but also roots the narrative in prophetic anticipation. The very first words you encounter set the stage by quoting Isaiah: "A voice of one calling in the wilderness." This is the prophet who first prepared the way for Jesus, echoing a divine plan established long before that moment in history.

Isaiah's writings were steeped in visions of hope and redemption for the Israelite people, establishing him as a leading voice among the prophets. In fact, the Book of Isaiah is often called the fifth Gospel due to its numerous references to messianic themes and the coming of the Lord. Sort of a biblical opening act, you might say! Interestingly, there are multiple passages across the **Three Synoptic Gospels**—Matthew, Mark, and Luke—that highlight both the significance and fulfillment of prophecies, underscoring the continuity of God's promises throughout time.

With the scene set by Mark—John the Baptist in the wilderness, adorned in camel’s hair and dining on locusts and wild honey—we get a raw and rugged introduction to a transformative religious movement. Mark's urgency in his narrative often presents Jesus in the context of action and power, embodying the very message conveyed by the prophets. So, while he’s introducing Jesus, he’s also giving a nod back to deep roots in Israel’s spiritual history, where each prophet contributes to the unfolding divine story. It's striking how a singular reference can connect the reader right back to centuries of tradition!