The answer is: Isaiah

Isa 40:3

In the Gospel of Mark, when the author introduces John the Baptist, they are quick to mention a reference to the words of Isaiah. This is significant not just because it substantiates the identity of John as a prophet, but it also sets the tone for the entire Gospel, filled with themes of prophecy and fulfillment. Isaiah 40:3 proclaims, “A voice cries out in the wilderness: 'Prepare the way of the Lord.'” This insistence on a voice calling from potentially barren places speaks volumes about the transformative nature of prophetic callings, beckoning people to a deeper relationship with something greater than themselves.

Interestingly, Isaiah isn’t just plucked out of thin air; he’s a heavyweight in the Biblical roster. His messages of hope and restoration are gems amidst the overflow of crisis and challenge in the scripture. The Gospel unveils this connectedness between the Old and New Testament, showcasing how stories and messages iterate through generations.

Fans of trivia might find it captivating that Mark’s Gospel is considered the first written document of its kind, believed to have been penned around 65-70 AD. Furthermore, the direct reference to Isaiah highlights a dramatic transition in religious thought that would echo through centuries, weaving into the broader narrative, where "the voice in the wilderness" resonates through the call of countless figures in scripture, reflecting a broader human experience of searching, wandering, and ultimately finding pathways to understanding. So next time you see a voice arise in silence, think of how the echo of Isaiah still speaks.