Matthew 3:3 cites Isaiah 40:3, using the word because
(or for
in the ESV) to show that John’s ministry had been foretold in the Old Testament. As God brought Israel to the Promised Land through the wilderness, so he will prepare a way for the Messiah in the wilderness. The preparation is for the whole of God’s people through the work of the herald (see Matthew 3:2; Isaiah 40:9–11). Mark 1:3 also cites Isaiah 40:3 to introduce John’s preaching of a gospel of repentance for the forgiveness of sins. Both Isaiah and John are concerned with the coming of Yahweh to a people prepared in their hearts to meet him.
Matthew here cites Isaiah 40:3. The subordinating conjunction because
here highlights the fact that the actions and preaching of John the Baptist had already been prophesied in the Old Testament. Just like the redemption from Egypt happened through the wilderness, so the path for the Lord is also finally prepared there as well. This prophecy is fulfilled in the work of John the Baptist, the harbinger of the coming King. His preaching shows that the preparations for the coming of the Messiah was not something that concerned him alone, but rather the people as a whole (see Matthew 3:2, Isaiah 40:9–11).1
This quotation from Isaiah marks the voice in the wilderness as the herald of none other than Yahweh himself. His coming signifies the coming of the kingdom of heaven. But his coming therefore also demands of the people that they repent of their ways, which may seem just to them, but which in reality is crooked in the eyes of God (for Isaiah 40:3 see also Mark 1:3).2
John the Baptist and his work was already prophesied by Isaiah. The value of this work is amplified by the fact that it is a fulfillment of a prophecy. Isaiah, after all, prophesied of the redemption that would be accomplished by the Servant of the Lord, the Messiah. For this reason John the Baptist had to exhibit all the characteristics described by the prophecy. Isaiah spoke of the coming of the Lord to his people in Christ. The coming of Christ the Messiah is also the coming of God.3
3 Jean est celui qui avait été annoncé par Esaïe, le prophète, lorsqu'il dit:C'est ici la voix de celui qui crie dans le désert:Préparez le chemin du Seigneur,Aplanissez ses sentiers.