Malachi 3:1

Behold, I will send My messenger, and he shall prepare the way before Me: and the Lord, whom you seek, shall suddenly come to His temple, even the messenger of the covenant, whom you delight in: behold, He shall come, says the LORD of hosts.

This prophecy is concerning John the Baptist and his role with respect to the coming of the Lord Jesus Christ. { see Matthew 11:10, Mark 1:2, Luke 7:27, Luke 1:76}

Malachi 4:5-6

5 Behold, I will send you Elijah the prophet before the coming of the great and dreadful day of the LORD:
6 And he shall turn the heart of the fathers to the children, and the heart of the children to their fathers, lest I come and smite the earth with a curse.

This prophecy likens Elijah to John the Baptist. {see Matthew 11:14, Luke 1:13-17}