Malachi’s message was spoken to people who had been returned by God from exile, but who had not wholly returned to God. Their priests were not truly messengers of God; their offerings were not worthy. Nonetheless, the message of the Lord delivered by Malachi is that, at long last, God will return to the temple he had abandoned before the exile, He will purify the sinners who set up the barrier to his presence and the relationship of God and people will be restored.
This sounds like a promise of the Messiah until we read in verse 4 that this promise is looking backward. This is a promise of restoration to the time of Moses when the covenant was first made, to the time of Solomon when God filled the temple with His presence, to a time when the people approached God only through priests, and atonement offerings were constantly required. The new covenant prophesied by Jeremiah is not mentioned here.
The Israelites to whom Malachi spoke could not have imagined that God would come to his people in person, or that He, himself, would be the temple, the perfect priest, the perfect, final offering of atonement, and that purification would be made through His suffering. They could not have imagined that He would offer a new covenant based on His grace rather than His law. Seeing ourselves in their place, but knowing Jesus, we are again astonished at God’s grace.