The prophet Esaias - The prophet Isaiah. Esaias is the Greek mode of writing the name. This passage is taken from Isaiah 40:3. It is here said to have been spoken in reference to John, the forerunner of Christ. The language is such as was familiar to the Jews. and such as they would understand. It was spoken at first with reference to the return from the captivity at Babylon. In ancient times, it was customary in the march of armies to send messengers, or pioneers, before them to proclaim their approach; to provide for them; to remove obstructions; to make roads, level hills, fill up valleys, etc. Isaiah, describing the return from Babylon, uses language taken from that custom. A crier, or herald, is introduced. In the vast deserts that lay between Babylon and Judea he is represented as lifting up his voice, and, with authority, commanding a public road to be made for the return of the captive Jews, with the Lord as their deliverer. “Prepare his ways, make them straight,” says he. The meaning in Isaiah is, “Let the valleys be exalted, or filled up, and the hills be levelled, and a straight, level highway be prepared, that they may march with ease and safety.” See the notes at Isaiah 40:3-4. The custom here referred to is continued in the East at the present time. “When Ibrahim Pasha proposed to visit certain places on Lebanon, the emeers and sheiks sent forth a general proclamation, somewhat in the style of Isaiah’s exhortation, to all the inhabitants, to assemble along the proposed route and prepare the way before him. The same was done in 1845, on a grand scale, when the present sultan visited Brousa. The stones were gathered out, the crooked places straightened, and the rough ones made level and smooth.” - The Land and the Book, Vol i. pp. 105, 106.
As applied to John, the passage means that he was sent to remove obstructions, and to prepare the people for the coming of the Messiah, like a herald going before an army on the march, to make preparations for its coming.