John Wesley on Jeremiah 49:39

But - We had the like promise as to Moab, chap.48:47, and as to Ammon, ver.49:6, the same latter days either signify after many days, or in the time of the Messiah. In the former sense it may refer to Cyrus, who conquered Persia. In the latter sense it refers to the spiritual liberty which some of these poor Heathens were brought into by the gospel. We read Acts 2:9, that some of the Elamites were at Jerusalem at pentecost, and were some of those converted to Christ.