When the Lord gave His words to the prophet Isaiah in Is. 40:3-5, in the literal sense it meant the anticipation of the return of the exiles from Babylon. It was a prophecy given by Isaiah to the Israelites who hardened their hearts and disobeyed the Lord. The Lord had to punish the Israelites for their wickedness and disobedience by allowing Nebuchadnezzar to destroy the city of Jerusalem and to bring them into captivity for seventy years. And Isaiah wrote this prophecy almost two hundreds years before the real event happened.
It is true that there was a need to prepare a way for the returnees from Babylon in the Syrian Desert, between Babylonia and Palestine. However, the prophet Isaiah exaggerated when he said, “Prepare ye the way of the Lord, make straight in the desert a highway for our God, every valley shall be exalted, and every mountain and hill be made low; and the crooked shall be made straight, and the rough places plain” (Is. 40:3-4). What Isaiah described here never occurred during the return of the exiles from Babylon.
Although Is. 40:3-5 seems to have been fulfilled when the returnees came back to their land, in reality it has not. God had seen and prepared this event as a picture or symbol for the coming of the Messiah. Lenski said, “The desert is, being used figuratively by Isaiah to denote the hindrances and obstacles which separate the people from Jehovah. Hence a road must be prepared through them, on which Jehovah was to come to His people in order to deliver them.” Thus, Is. 40:3-5 is the heart of the message heralding the coming of the Messiah.
Since references were made to Is. 40:3-5 in Matt. 3:3; Mark 1:3 and Luke 3:4-6, there is no doubt that Is. 40:3-5 was fulfilled in the ministry of John the Baptist. John himself said deliberately to those who desired to know who he was, “the voice of one crying in the wilderness, Make straight the way of the Lord as said the prophet Esaias” (John 1:23). John the Baptist was a herald who shouted in the wilderness, preaching baptism for the remission of sins. In other words the deliverance of the Israelites from Babylon was only a type for our redemption in the Lord Jesus Christ.
The Lord had prepared John the Baptist to be a herald for the coming of Jesus Christ. He must prepare the way for Him so that when He comes to bring the message of salvation, the people would receive it with gladness and recognize Him as the Messiah. The world that is full of wickedness and depravity must know the Lord Jesus Christ that they may have eternal life. For apart from knowing Him as their Lord and Saviour, they will be lost in sins. John the Baptist knew and saw crisis in the ruined lives of those who lived in the time of Jesus Christ. The fact was that though he had proclaimed what the Lord had commanded him to do as a herald, few people responded to his calling. The hardening of the hearts of the people had caused them to continue living in their sins.
Thus, John the Baptist had a great responsibility during his ministry as a herald of the Messiah. He did not exalt himself as a Prophet as he realized that he was the way-preparer. As Hendriksen rightly opines, "He was to be the Lord's "voice" to the people, all of that but not more than that (cf. John 3:22-30). As such he must not only announce Christ's approach and presence but also urge the people to prepare the way of the Lord, that is, by God's grace and power to effect a complete change of mind and heart. This applies that they must make straight his paths, meaning that they must provide the Lord with a ready access into their hearts and lives. They must make straight whatever was crooked, not in line with God's holy will. They must clear away all the obstacles which they had thrown into his path; such obstructions as self-righteousness and smug complacency ("We have Abraham as our father," Matt. 3:9), greed, cruelty, slander, etc. (Luke 3:13,14)."
It is clearly seen in the Old Testament that a herald of Christ had been foretold in order that His people might accept and realize the truth that the Messiah, the Christ, was the Lord Jesus. Everyone who believes in Him will see Him in the glorious day when He returns in His second Coming.
