John Calvin Commentary Malachi 3:4

"Then shall the offering of Judah and Jerusalem be pleasant unto Jehovah, as in the days of old, and as in ancient years." — Malachi 3:4 (ASV)

This verse shows that, although he had just spoken of the sons of Levi, he still had regard for the whole people. But he meant to confine to the elect what should not have been extended to all, because there were among the people, as we have seen and will soon see again, many who were reprobates; indeed, the greater part had fallen away. This is the reason why the Prophet especially addresses the few remaining who had not fallen away.

But he names Judah and Jerusalem, because that tribe had returned to their own country, and sacrifices were offered at Jerusalem—though not with the splendor of ancient times, as their situation had greatly deteriorated among those miserable exiles. Therefore, to encourage the faithful, the Prophet says that although the temple was then humble, and the worship of God as then performed was unadorned and lowly, there was still no reason for the Levites or for others to lose heart. The Lord would again restore the glory of His temple and truly show that what men viewed with scorn was approved by Him.