You have wearied the LORD with your words. Yet you say, “How have we wearied Him?” In that you say, “Everyone who does evil is good in the sight of the LORD, and He delights in them,” or, “Where is the God of justice?”

“Behold, I am going to send My messenger, and he will clear the way before Me. And the Lord, whom you seek, will suddenly come to His temple; and the messenger of the covenant, in whom you delight, behold, He is coming,” says the LORD of hosts.

“But who can endure the day of His coming? And who can stand when He appears? For He is like a refiner’s fire and like fullers’ soap. He will sit as a smelter and purifier of silver, and He will purify the sons of Levi and refine them like gold and silver, so that they may present to the LORD offerings in righteousness. Then the offering of Judah and Jerusalem will be pleasing to the LORD as in the days of old and as in former years.”
Malachi 2:17–3:4

Malachi was last of the postexilic prophets, and the last prophet in Judah for over 450 years until John the Baptist begins to preach—and when the angel announces John’s coming birth to Zacharias, he will quote from the very last verse in Malachi:

“Behold, I am going to send you Elijah the prophet before the coming of the great and terrible day of the LORD. He will restore the hearts of the fathers to their children and the hearts of the children to their fathers, so that I will not come and smite the land with a curse.”
Malachi 4:5

This will be John’s purpose and calling:

But the angel said to him, “Do not be afraid, Zacharias, for your petition has been heard, and your wife Elizabeth will bear you a son, and you will give him the name John. You will have joy and gladness, and many will rejoice at his birth. For he will be great in the sight of the Lord; and he will drink no wine or liquor, and he will be filled with the Holy Spirit while yet in his mother’s womb. And he will turn many of the sons of Israel back to the Lord their God. It is he who will go as a forerunner before Him in the spirit and power of Elijah, to turn the hearts of the fathers back to the children, and the disobedient to the attitude of the righteous, so as to make ready a people prepared for the Lord.”
Luke 1:13–17

Jesus Himself identified John as the messenger of Malachi 3:1:

As these men were going away, Jesus began to speak to the crowds about John, “What did you go out into the wilderness to see? A reed shaken by the wind? But what did you go out to see? A man dressed in soft clothing? Those who wear soft clothing are in kings’ palaces! But what did you go out to see? A prophet? Yes, I tell you, and one who is more than a prophet. This is the one about whom it is written,

‘Behold, I send My messenger ahead of You,
Who will prepare Your way before You.’

Truly I say to you, among those born of women there has not arisen anyone greater than John the Baptist! Yet the one who is least in the kingdom of heaven is greater than he. From the days of John the Baptist until now the kingdom of heaven suffers violence, and violent men take it by force. For all the prophets and the Law prophesied until John. And if you are willing to accept it, John himself is Elijah who was to come. He who has ears to hear, let him hear.”
Matthew 11:7–14

Do you know what the name Malachi means? Gleason Archer writes:

The most reasonable explanation for the meaning of Malachi (Mal’ ākī, Hebrew) is that it is hypocoristic [an endearing diminutive] for the full form Mal’ ak-Yah, or Messenger of Jehovah.¹

So Malachi, Messenger of Jehovah, prophesies of John, the messenger who will prepare the way— ‘to turn the hearts of the fathers back to the children, and the disobedient to the attitude of the righteous, so as to make ready a people prepared for the Lord’, Jesus the Christ, Messiah.

__________
Архангел Гавриил поражает Захарию немотой The Angel Appears to Zacharias, Alexander Andreyevich Ivanov 1824.
¹Gleason L. Archer, Jr., “Postexilic Prophets: Haggai, Zechariah, Malachi,” A Survey of Old Testament Introduction (Moody Press, Chicago IL: 1966, 1974) 430.