What does Malachi 3:1 mean?

Look, I'm sending my messenger to clear the way ahead of me. Then suddenly, the Lord you're looking for will show up at His temple. The messenger of the agreement you want so badly—he's coming, says the Lord who rules over everything. Malachi 3:1 - Modern Text Bible

(God promises to send someone to prepare the way for His own arrival, hinting at a coming time of reckoning and hope.)