In Malachi 3:17 ff the word “day” is used 4 times for “the day of the LORD”. There seem to be a lot of events that are to occur in this day. Walter Kaiser suggests the concept of a generic prophecy that form a collective event made up of a number of happenings that occur successively. So then “Elijah” in 4:5 could represent Elijah as the head of the prophets, John the Baptist (Matthew 17:13) or Elijah at the end of history (Revelation 11:3). Picking just one event to be the fulfillment does not do justice to this passage. Let me reproduce here Kaiser’s discussion:
“…for each of five Old Testament prophets working in four separate centuries, that day was ‘near’ and ‘at hand’ (Ninth Century Obadiah 15; Joel 1:15; 2:1; Eighth Century, Is 13:6; seventh Century Zeph 1:7,14; and Sixth Century, Ezk 30:3). Each of these prophets also saw immediate events in his own generation as very much part of the same ‘day of the Lord’; …
This presents us a three-way puzzle; that day is viewed as one day, that is a collective event embracing a number of distinct happenings occurring successively in history. But if we were to limit the meaning of that day to any one of these events, it would appear to be exaggerated and unfulfilled since on one occurrence, until the final one in the succession, exhausts the meaning. The prophecy must be viewed as being successively fulfilled through a number of events in history, all of which depict, now one and now another aspect of the final and climactic fulfillment.”
Walter C. Kaiser, Jr; Malachi: God’s unchanging Love, 1984, Baker, Grand Rapids, p. 102.
I find this principle helpful in understanding prophetic literature, which has much more interest in what is to happen, than in when it will happen.