God answers the accusation, but not the way anyone expected. He does not explain the drought. He does not announce a timeline for removing Persia. He promises people. First a messenger to prepare the way, identified later in Malachi 4:5 as Elijah and fulfilled in John the Baptist. Jesus makes that identification himself, quoting this exact verse over his cousin in Matthew 11:10. Then the Lord whom you seek, who is also the messenger of the covenant, one person, not two: Jesus Christ.
Notice what he came to do with the temple they were so disappointed in. He visited it, yes. But in John 2:19-22 he says destroy this temple and in three days I will raise it up, and John tells us plainly that he was speaking about the temple of his body. The building whose lack of glory had become the evidence for their complaint was never the point. It was a pointer. And in Matthew 26:26-28 at the last supper, he takes the cup and calls it his blood of the covenant, poured out for many for the forgiveness of sins. The messenger of the covenant became its mediator, a theme the letter to the Hebrews returns to again and again.
There is a word in this verse worth sitting with: suddenly. They had already waited a hundred years, and four hundred more of silence lay ahead. Yet when he came, he came suddenly. God’s timing is not a negotiation, and the length of the wait says nothing about the certainty of the promise.
They asked where the God of justice was. God answered by telling them a Savior was coming. That is not evasion. That is diagnosis. Their deepest problem was never Persia.