John the Baptist’s message is: "Repent, for the kingdom of heaven is at hand" Matthew 3:2. Matthew also connects John’s ministry to the "voice" preparing the Lord’s way Matthew 3:3.
Matthew introduces John the Baptizer suddenly “in those days” as a preacher in Judea’s wilderness. John’s message is brief and urgent: people should repent because “the Kingdom of Heaven” is near. Matthew then frames John’s appearance as the fulfillment of Isaiah’s words about a lone voice in the wilderness calling for road-preparation for the Lord. After narrating Jesus’ origins and early life, Matthew pivots to the start of public ministry by bringing in John as the first public herald. The wording “in those days” does not specify a date; it functions as a transition into the next phase of the story.
Matthew shifts from Jesus’ childhood story to the start of public events by introducing John “in the wilderness of Judea.” John is presented first as a preacher with a short, direct message: people should repent because “the Kingdom of Heaven” has come near (explicit in verse 1–2; “near” is the idea in near).
A careful answer keeps the immediate passage, the book's argument, and the whole-Bible storyline together, so the question is answered in context instead of as a detached idea.
Start with Matthew 3:2, then read the surrounding section so the answer stays connected to the passage's flow.
2"Repent, for the Kingdom of Heaven is at hand!"