My messenger
Whether Malachi's messenger is John the Baptist or Elijah, whether the Lord's coming to the temple is the first advent or a future judgment, and how Mark's combined citation is read.
Malachi 3:1-5
1“Behold, I send my messenger, and he will prepare the way before me; and the Lord, whom you seek, will suddenly come to his temple; and the messenger of the covenant, whom you desire, behold, he comes!” says Yahweh of Armies.
2“But who can endure the day of his coming? And who will stand when he appears? For he is like a refiner’s fire, and like launderers’ soap;
3and he will sit as a refiner and purifier of silver, and he will purify the sons of Levi, and refine them as gold and silver; and they shall offer to Yahweh offerings in righteousness.
4Then the offering of Judah and Jerusalem will be pleasant to Yahweh, as in the days of old, and as in ancient years.
5I will come near to you to judgment; and I will be a swift witness against the sorcerers, and against the adulterers, and against the perjurers, and against those who oppress the hireling in his wages, the widow, and the fatherless, and who deprive the foreigner of justice, and don’t fear me,” says Yahweh of Armies.
Mark 1:2-4
2As it is written in the prophets, “Behold, I send my messenger before your face, who will prepare your way before you:
3the voice of one crying in the wilderness, ‘Make ready the way of the Lord! Make his paths straight!’ ”
4John came baptizing in the wilderness and preaching the baptism of repentance for forgiveness of sins.
What each tradition says
Rabbinic / Midrashic
According to Singer and Guttmacher, the messenger will come in the person of Elijah. Elijah will regenerate the people and restore them to union with Yhwh.
Isidore Singer, Adolf Guttmacher, Malachi, Book of (Jewish Encyclopedia, 1901-1906) — 'The messenger of Yhwh and the Last Judgment' (on Malachi 3:1 / 3:23)
Patristic
Irenaeus says the beginning of the Gospel plainly quotes the holy prophets and points out the Father of our Lord Jesus Christ, confessed as God and Lord. He had promised to send His messenger before His face; that messenger was John, crying in the wilderness in the spirit and power of Elias.
Irenaeus, Against Heresies, Book III, ch. X, §5 (ANF vol. 1, ed. Roberts & Donaldson) — Book III, Ch. X, §5 — on Mark 1:2-3 / Malachi 3:1 ('my messenger ... John')
Catholic
Haydock’s commentary takes “my angel” to mean John the Baptist, the messenger of God and forerunner of Christ. His purity and office procure him this title. Afterwards Christ himself shall come, for the ruin and resurrection of many.
George Leo Haydock, George Haydock's Catholic Bible Commentary (1859) — Note on Malachi 3:1 ('my angel ... the messenger of the covenant')
Orthodox
Chrysostom says Christ called John “Elias” because they shared a community of office, not because John was the Elijah meant by the prophet. The prophet’s added country, “the Tishbite,” guards against taking his prophecy as referring to John.
John Chrysostom, Homilies on the Gospel of St. Matthew, Homily LVII (NPNF ser. 1, vol. 10, trans. George Prevost) — Homily LVII, on Matt 17:10-13 (Elijah / John 'by their community of office')
Reformed / Protestant
Calvin says Malachi 3:1 ought doubtless to be understood of John the Baptist. Christ himself so explains it, and no better interpreter can be found. Since John was Christ's messenger, the beginning of the verse can apply to no other person.
John Calvin, Commentaries on the Twelve Minor Prophets, vol. 5: Zechariah, Malachi (trans. John Owen; Calvin Translation Society) — Commentary on Malachi 3:1 ('Behold, I send my messenger')
Evangelical
Wesley identifies Malachi’s messenger as John the Baptist and the Lord as the Messiah. He says the Lord comes suddenly after his forerunner, to his temple, which was the second temple in Jerusalem lately built by Zerubbabel and Joshua. Those who truly fear God long and wait for this Lord.
John Wesley, Explanatory Notes upon the Old Testament — Notes on Malachi 3:1