What does Malachi 3:18 mean?
Verses 16 and 17 described the reaction of those who responded correctly to Malachi's warnings. God promises to remember their faithfulness. This is an important vow, since the immediate context is one of severe judgment. Even though good people are often caught up in the consequences of other people's sins, God does distinguish between those who follow Him and those who do not.Malachi's promised judgment is meant, in part, to show the world this exact divide. God's coming retribution will demonstrate which people belong to God and which people defy Him. This will not be the first such distinction made by God. God's plagues during the Exodus were meant, primarily, to show His superiority over the gods of Egypt. Other miracles during that time were dependent on the cooperation of the people—so those who obeyed were distinguished from those who rebelled.
The brief passage marked as chapter 4 will continue this message of judgment and promise. As with the end of chapter 3, God's prediction includes both wrath for the wicked and protection for the righteous.