I have to agree with Resurrection33, Superdave and Crazy4GODword, this is speaking of John the Baptist.
Malachi 3:1
BEHOLD, I will send my messenger, and he shall prepare the way before Me: and the Lord, whom ye seek, shall suddenly come to His Temple, even the Messenger of the Covenant, whom ye delight in: behold He shall come, saith the LORD of Hosts.
Jesus is the Messenger of the Covenant (Hebrews 8:5-13). And this passage in Malachi 3:1. is referring also to Isaiah 40:3-8. A interesting fact in the Jewish Tanakh Malachi 3:1 is the beginning of Chapter 3 and what we have in the Christian Old Testament as Malachi 4:5-6, is in the Tanakh Malachi 3:22-23. so this chapter in the Tanakh opens with the Jesus Christ and John the Baptist and IMO end with Jesus Christ and John the Baptist.
As for your question as to why does Malachi say earth, instead of land. Earth is correct but so is land. For God woud destroy the land, and the earth which the Jewish nation was part of, til the time of the Gentile was fulfilled (Luke 21:24), for Jerusalem as of around 1967 is again a part of Israel. Because Jesus was rejected by the Jews and they did not accept the message of Elijah (Matthew 11:12-19) God's wrath would be poured out on them (I Thessalonians 2:14-16). God would destroy the Jewish Temple for after Christ sacrifice the Temple in Jerusalem was no longer God's, for we as believers have receive the blessing of receiving the Holy Spirit thus making us the True Temple of God (I Corinthians 3:16; 6:19-20). So Christ Jesus can not come to the Jewish Temple anymore. For after Christ sacrifice for our sins there remaineth no more sacrifice for sin (Hebrews 10:14, 18). And because the Jews continue to offer the Old Covenant sacrifice after Christ Resurrection God's Wrath was to be poured out on them (Hebrews 10:28-31).
Daniel 9:27 (The Tanakh)
During one week He will make a firm covenant with many. For half a week He will put a stop to the sacrifice and the meal offering. At the corner [of the altar] will be an appalling abomination until the decreed destruction will be poured down upon the appalling thing.
Notice Daniel said at the corner {of the altar} will be an appaling abomination until the decreed destruction will be poured down. The altar where the Jews still offer animal sacrifices before 70AD, for something God through His Son had finished once and for all (John 19:30). This would truly be an abomination to say an animal blood was Just as good as Jesus' Blood, would it not.
My apologies for the long post.