God would send Elijah the prophet in order to help divert the curse God was sending on the land.
In context “the land” most likely refers to the land of Israel since Malachi is speaking to Israel,
but the application would extend to the lands of any nation not heeding the words.

John the Baptist was the prophet who filled the role of Elijah (Luke 1:16) when he announced the coming of the Lord. If Jesus had been received by the Jewish nation they could have avoided the
70 AD destruction of their land that came by the hands of the Romans. The gospel period was a
day of the coming of the Lord. But, this verse talks about “that great and dreadful day of the Lord” which is the day of the Lord’s return. John the Baptist announced Jesus as a lamb coming to
“take away the sin of the world.” (John 1:29) The next Elijah-like prophet will announce Jesus
as a coming lion retuning to judge sin and to “strike the land with total destruction.” Throughout Christian history many commentators consider these verses in Malachi to be referring to the
literal return of Elijah to the earth since he was translated from the earth, but not separated
from his body. (2 Kings 2) This account of Elijah is combined with the similarly mysterious
departure of Enoch whose body was also taken, and not found.  (Genesis 5:24; Hebrews 11:5) Together Elijah and Enoch are often considered to be the two witnesses that stand powerfully
against the anti-christ before the Lord returns. (Revelation 11:1-14)

The Jews of Jesus day where also looking for the return of Elijah as indicated by the disciple’s question:

“The disciples asked him, “Why then do the teachers of the law say that Elijah must come first?” Jesus replied, “To be sure, Elijah comes and will restore all things. But I tell you, Elijah has already come, and they did not recognize him.”    
- Matthew 17:10-12

The word translated “total destruction” or “curse” is the Hebrew word “herem.” It refers to devoting people and things to the Lord for total destruction or as a burnt offering. The practice of applying
this word is seen in the destruction of the Canaanites by Joshua, specifically, at the fall of Jericho.
This verse closes the Old Testament. After the days of Malachi (515-490 BC) there were no
prophets sent by God until John the Baptist began to preach in 26 AD.

Malachi states that the prophet who goes before the Lord will “turn the hearts of the parents to
their children,” but also says, “the hearts of the children to their parents.” What is to be
understood in this statement? It is possible that the children are to return their hearts to the
faith of their fathers, the patriarchs Abraham, Isaac and Jacob. (See Elijah tell the children of
Israel to “turn their hearts back again” in 1 Kings 18:37b.) And, the “fathers” who are to turn their hearts to the children refer to the forefathers of Israel who seemed to always rebel against the
work of God (see Stephen’s speech in Acts 7). These forefathers need to return to the faith
and trust of a child following the Lord.