As it is written in Isaiah the prophet,
"Behold, I send my messenger before thy face,
who shall prepare thy way;
the voice of one crying in the wilderness:
Prepare the way of the Lord,
make his paths straight -"
Bede - Being about to write his Gospel, Mark rightly puts first the testimonies of the Prophets, that he might notify to all, that what he should write was to be received without scruple of doubt, in that he shewed that these things were beforehand foretold by the Prophets. At once, by one and the same beginning of his Gospel, he prepared the Jews, who had received the Law and the Prophets, for receiving the grace of the Gospel, and those sacraments, which their own prophecies had foretold; and he also calls upon the Gentiles, who came to the Lord by publishing of the Gospel, to receive and venerate the authority of the Law and the Prophets; whence he says, "As it is written in the prophet Isaiah, Behold, etc."
Jerome, Hierom. ad Pammach, Epist 57 - But this is not written in Isaiah, but in Malachi, the last of the twelve prophets.
Pseudo-Chrys., Vict. Ant. e Cat. in Marc. - But it may be said that it is a mistake of the writer. Otherwise it may be said that he has compressed into one, two prophecies delivered in different places by two prophets; for in the prophet Isaiah it is written after the story of Hezekiah, "The voice of one crying in the wilderness;" but in Malachi, "Behold, I send mine angel."
The Evangelist therefore, taking parts of two prophecies, has put them down as spoken by Isaiah, and refers them here to one passage, without mentioning, however, by whom it is said, "Behold, I send mine angel."
Pseudo-Aug., Quaest. nov. et vet. Test. lvii - For knowing that all things are to be referred to their author, he has brought these sayings back to Isaiah, who was the first to intimate the sense.
Lastly, after the words of Malachi, he immediately subjoins, "The voice of one crying in the wilderness," in order to connect the words of each prophet, belonging as they do to one meaning, under the person of the elder prophet.
Bede - Or otherwise, we must understand, that although these words are not found in Isaiah, still the sense of them is found in many other places, and most clearly in this which he has subjoined, "The voice of one crying in the wilderness." For that which Malachi has called, the angel to be sent before the face of the Lord, to prepare His way, is the same thing as Isaiah has said is to be heard, "the voice of one crying in the wilderness, saying, Prepare ye the way of the Lord."
But in each sentence alike, the way of the Lord to be prepared is proclaimed. It may be, too, that Isaiah occurred to the mind of Mark, in writing his Gospel, instead of Malachi, as often happens; which he would, however, without doubt correct, at least when reminded by other persons, who might read his work whilst he was yet in the flesh; unless he though that, since his memory was then ruled by the Holy Spirit, it was not without a purpose that the name of one prophet had occurred to him instead of another. For thus whatsoever things the Holy Spirit spoke by the prophets are implied each to have belonged to all, and all to each.
Jerome - By Malachi, therefore, the voice of the Holy Spirit resounds to the Father concerning the Son, who is the countenance of the Father by which He has been known.
Bede - But John is called an angel not by community of nature, according to the heresy of Origen, but by the dignity of his office; for angel in Greek is in Latin, nuntius (note: messenger), by which name that man is rightly called, who was sent by God, that he might bear witness of the light, and announce to the world the Lord, coming in the flesh; since it is evident that all who are priests may be their office of preaching the Gospel be called angels, as the prophet Malachi says, "The lips of the priest keep knowledge, and they seek the law at his mouth, because he is the Angel of the Lord of hosts." [Malachi 2:7]
Theophylact - The Forerunner of Christ, therefore, is call an angel, on account of his angelic life and lofty reverence. Again, where he says, "Before thy face," it is as if he said, Thy messenger is near thee: whence is shewn the intimate connection of the Forerunner with Christ; for those walk next to kings who are their greatest friends.
There follows, "Who will prepare thy way before thee."
For by baptism he prepared the minds of the Jews to receive Christ.
Pseudo-Jerome - Or, "the way of the Lord," by which He comes into men, in penitence, by which God comes down to us, and we mount up to Him. And for this reason the beginning of John's preaching was, "Repent ye."
Bede - But as John might be called an angel, because he went before the face of the Lord by his preaching, so he might also be rightly called a voice, because, by his sound, he preceded the Word of the Lord.
Wherefore there follows, "The voice of one crying, etc."
For it is an acknowledged thing that the Only-Begotten Son is called the Word of the Father, and even we, from having uttered words ourselves, know that the voice sounds first, in order that the word may afterwards by heard.
Pseudo-Jerome - But it is called "the voice of one crying," for we are wont to use a cry to deaf persons, and to those afar off, or when we are indignant, all which things we know applied to the Jews; for "salvation is far from the wicked," and they "stopped their ears like deaf adders," and deserved to hear "indignation, and wrath, and tribulation" from Christ.
Pseudo-Chrys., Vict. Ant. e Cat. in Marc. - But the prophecy, by saying, "In the wilderness," plainly shews that the divine teaching was not in Jerusalem, but in the wilderness, which was fulfilled to the letter by John the Baptist in the wilderness of Jordan, preaching the healthful appearing of the Word of God.
The word of prophecy also shews, that besides the wilderness, which was pointed out by Moses, where he made paths, there was another wilderness, in which it proclaimed that the salvation of Christ was present.
Pseudo-Jerome - Or else the voice and the cry is in the desert, because they were deserted by the Spirit of God, as a house empty, and swept out; deserted also by prophet, priest, and king.
Bede - What he cried is revealed, in that which is subjoined, "Prepare ye the way of the Lord, make his paths straight." For whosoever preaches a right faith and good works, what else does he but prepare the way for the Lord's coming to the hearts of His hearers, that the power of grace might penetrate these hearts, and the light of truth shine in them? And the paths he makes straight, when he forms pure thoughts in the soul by the word of preaching.
Pseudo-Jerome - Or else, "Prepare ye the way of the Lord," that is, act out repentance and preach it; "make his paths straight," that walking in the royal road, we may love our neighbours as ourselves, and ourselves as our neighbours. For he who loves himself, and loves not his neighbour, turns aside to the right; for many act well, and do not correct their neighbour well, as Eli.
He, on the other hand, who, hating himself, loves his neighbour, turns aside to the left; for many, for instance, rebuke well, but act not well themselves, as did the Scribes and Pharisees.
"Paths" are mentioned after the "way" because moral commands are laid open after penitence.
Theophylact - Or, the "way" is the New Testament, and the "paths" are the Old, because it is a trodden path. For it was necessary to be prepared for the way, that is, for the New Testament; but it was right that the paths of the Old Testament should be straightened.
- text taken from Catena Aurea - Gospel of Mark by Saint Thomas Aquinas, translated by William Whiston, 1842