Five centuries earlier, Malachi (since the word means messenger, we can't be sure if Malachi is a prophet's name or a description of his function) spoke to the faithful remnant--or, perhaps to the first returning exiles. He told them that they needed to change a lot of things from the ways they had been behaving before the destruction by Assyria of Jerusalem and the temple, "You have not been faithful in worship or in your dealings with each other. Repent."
In the passage from this week's lectionary, Malachi warns that the Day of the Lord is coming and that this arrival is not good news for evildoers. But, he promises that those who have been faithful will be rewarded.
At the time of exile, they could look back and contemplate rather they really had spent much effort on caring for widows and orphans, or being honest in business, and worrying about the welfare of the stranger. And at the time of Jesus, they also could also review whether they had followed those commands of the Lord or whether they had focused more on their own welfare. And, of course, here we are, with the same opportunities and temptations.
Jesus said, "For some of you, the sun of righteousness shall rise, with healing in its wings." Here's what Allen & Williamson, In Preaching the Old Testament, say about this assurance:
The good news in Malachi is that, although we sin long and hard, God never gives up on us. God's steadfast love is an adamant love, a love that will not let us go....