The answer is: Isaiah

Isa 40:3

In the Gospel of Mark, it’s pretty striking that the first prophet who gets mentioned is no other than Isaiah. He lays down a significant call for someone to prepare the way for the Lord, echoing from Isaiah 40:3. This isn't just a random inclusion; it mirrors the Gospel's bigger message about Jesus’ role and mission. By starting with Isaiah's prophetic words, Mark is making a connection between Jesus and the longstanding tradition of Israel’s prophets—reestablishing how Jesus fits into the grand narrative of salvation.

Isaiah's ministry was set against a backdrop of hope during turbulent times for Israel. He spoke to a people longing for rescue and reassured them about future glory, emphasizing themes of redemption that resound throughout the New Testament. Fun fact: Isaiah is such a central figure that his writings are quoted all over the New Testament; in a way, he acts like a prophetic bridge connecting the two Testaments.

Mark not only establishes Jesus as the awaited Messiah but positions him in the larger story of Israel and their longing for God's kingdom. The reference signifies a fulfillment of promises made long before Christ arrived, showcasing an engaging sense of continuity. It reminds readers of the anticipatory hopes of a broken world and how those hopes meet in surprising and incredible ways in Christ.