Malachi 3:2-6

Verse 2

But who may abide the day of his coming? - Only they who shall believe on his name; for they that will not, shall be blinded, and the unbelieving nations shall be destroyed by the Romans.

Like fuller's soap - כברית keborith, from ברר barar, to cleanse, any thing that deterges. Kali, or fern ashes, or such things. I doubt whether the composition which we call soap, was known in ancient times.
Verse 3

He shall sit as a refiner - Alluding to the case of a refiner of metals, sitting at his fire; increasing it when he sees necessary, and watching the process of his work.

The sons of Levi - Those who minister in their stead under the New covenant, for the Old Levitical institutions shall be abolished; yet, under the preaching of our Lord, a great number of the priests became obedient to the faith, Act 6:7; and, as to the others that did not believe, this great Refiner threw them as dross into the Roman fire, that consumed both Jerusalem and the temple.
Verse 5

I will come near to you to judgment - And what fearful cases does he get to judge! Sorcerers, adulterers, false swearers, defrauders of the wages of the hireling, oppressors of widows and orphans, and perverters of the stranger and such as do not fear the Lord: a horrible crew; and the land at that time was full of them. Several were converted under the preaching of Christ and his apostles, and the rest the Romans destroyed or carried into captivity.
Verse 6

I am the Lord, I change not - The new dispensation of grace and goodness, which is now about to be introduced, is not the effect of any change in my counsels; it is, on the contrary, the fulfillment of my everlasting purposes; as is also the throwing aside of the Mosaic ritual, which was only intended to introduce the great and glorious Gospel of my Son.

And because of this ancient covenant, ye Jews are not totally consumed; but ye are now, and shall be still, preserved as a distinct people - monuments both of my justice and mercy.
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