John Gill's Exposition of the Whole Bible
Malachi 3:18
Then shall ye return,.... Either the wicked, who will be "converted" z, as some render the word, and will have a different view of things, and change their minds and language; or they that feared the Lord, who at the time before spoken of will have a new turn of thought, and another and clear discerning of persons and things, and better judge of the dispensations of Providence: some that refer this to the resurrection of the dead, and the last judgment, understand it, as Abarbinel does, of the returning of souls to their bodies, when indeed the difference between persons after described will be very discernible; but it seems to refer to the time of Christ's first coming, and Jerusalem's destruction:
and discern between the righteous and the wicked; the difference between such who are really and truly righteous, who are here meant, even such who believe in Christ, and are justified by his righteousness; and those that are wicked, as all by nature are: though sometimes this character designs the more profane and abandoned, and even professors of religion; the difference between these is not always easily discerned; as for the righteous, they are not known and discerned by the world; and by reason of afflictions, temptations, and sins, they are apt to judge wrong of themselves; and sometimes are so left to fall into sin, that they look like others: and there are wicked men under the appearance of righteous men, as were the Scribes and Pharisees in Christ's time; but by the destruction that came upon them, and the preservation of such as believed in Christ, it was discernible who were wicked, and who were righteous; indeed, at the last day, this difference will be more visible; in the bodies of the righteous, which will be raised glorious, when those of the wicked will not; in their souls, having on the wedding garment, the robe of Christ's righteousness, and perfectly holy; and in their situation, being set at Christ's right hand, and the wicked at his left; and by the characters that will be given of them by the Judge, and the different sentences passed and executed on them:
between him that serveth God and him that serveth him not; that is, between such persons that serve the Lord, and him only, privately and publicly, in righteousness and true holiness, in spirit and in truth, with faith and fervency, with reverence and fear, heartily and willingly, seeking his glory, without any dependence on their services; and those that are ungodly, or only outwardly serve the Lord, for sinister ends, and with selfish views, and according to their own inventions, and the traditions of men, and not the will of God, as the Scribes and Pharisees; between whom, and Christ's sincere disciples and followers, the awful day, described in the next chapter Malachi 4:1, will make a manifest difference.
z ושבתם "et convertemini", Cocceius, Gussetius, so Pagninus, Montanus; "conversi", Drusius, Junius Tremellius.