Jewish readers recognized Isaiah 40 as a great announcement of restoration after exile. The prophet calls for a highway to be prepared because Israel's God is coming to his people.
John's wilderness ministry evokes this restoration setting. Matthew's use of the passage identifies Jesus' arrival with the promised divine visitation in a way that exceeds a simple claim that Jesus is another prophet.
Isaiah 40:3 calls for preparation of 'the way of the LORD' and a straight highway 'for our God.' The following verses announce that the glory of the LORD will be revealed and that God comes with power to shepherd his people.
By applying the preparatory voice to John and narratively directing John's ministry toward Jesus, Matthew places Jesus in the position occupied by the coming LORD in Isaiah's prophecy.
John announces that the kingdom of heaven has drawn near. Matthew immediately explains John's identity with Isaiah's wilderness voice. The person whose way John prepares in the Gospel is Jesus, who appears for baptism and then begins the messianic mission.
This is an example of a Gospel writer communicating Jesus' identity through scriptural fulfillment rather than through a modern abstract formula.
The strength of the passage lies in the transfer of an Old Testament YHWH text into the narrative of Jesus. Isaiah speaks of preparing for the LORD; Matthew depicts John preparing for Jesus.
This does not erase the distinction between Father and Son. Rather, it is consistent with the New Testament pattern of including Jesus within roles and scriptural descriptions belonging to the God of Israel.
People from Jerusalem, Judea, and the Jordan region go out to John, confess sins, and receive baptism.