By John's baptism the way was prepared for Jehovah the Lord to come down into the world and carry out redemption.
We read in Malachi:
Look, I am sending my messenger who will prepare the way before me, and suddenly the Lord whom you seek will come to his temple, and the messenger of the covenant whom you desire. Who will endure the day of his coming, and who will stand firm when he appears? Mal. 3:1, 2.
Look, I shall send you the prophet Elijah before the great and terrible day of Jehovah comes, so that I may not come and strike the land with a curse. Mal. 4:5, 6.
When his father Zechariah prophesied about his son John:
You, my child, will be called the prophet of the Most High, you will go before the face of the Lord to prepare His ways. Luke 1:76.
The Lord Himself said about John the Baptist:
He it is of whom it was written, Look, I am sending my messenger before your* face, who will prepare your way in front of you. Luke 7:27.
It is clear from these passages that John was the prophet who was sent to prepare the way for Jehovah God, so that He could come down into the world and carry out redemption. It is also clear that he prepared that way by baptising, and by announcing the Lord's coming; and that but for that preparation all there would have been struck with a curse and would have perished.
* Latin: 'my face', corrected in the Author's copy.