What does Malachi 4:5 mean?

Malachi chapter 4 describes an impending judgment from God. This will occur on "the day" of ultimate reckoning. Malachi 3:1 has already promised a messenger who will prepare for the arrival of Messiah. That same verse has often been linked to the predicted return of Elijah from this verse. While Moses is representative of the Law, Elijah is representative of the prophets. John the Baptist would fulfill the "messenger" prophecy of Malachi 3:1 (Isaiah 40:3; John 1:23). Yet, he specifically denied that he was the prophesied "Elijah" of this verse in Malachi (John 1:21). The Gospels only refer to John the Baptist's ministry as "in the power of Elijah" (Luke 1:17), and only for those receptive to the message (Matthew 11:14). Jesus noted that Elijah was still to come (Matthew 17:11), a statement made after John the Baptist's death.

It's plausible to interpret this as a reference to John the Baptist, and his denial as nothing more than excessive humility. Or, that Malachi has in mind a separate, later reappearance of Elijah, as in Revelation 11:1–13. This moment in the end times might involve Elijah himself or someone, like John the Baptist, who comes "in his power." Both Christian and Jewish scholars frequently debate the specifics of this passage. Ultimately, we won't know exactly which is correct until all things have been revealed.