As thou didst rejoice at the inheritance of the house of Israel, because it was desolate, so will I do unto thee: thou shalt be desolate, O mount Seir, and all Idumea, even all of it: and they shall know that I am the LORD.

As thou didst rejoice over the inheritance of the house of Israel, because it was desolate, so will I do unto thee: thou shalt be desolate, O mount Seir, and all Edom, even all of it; and they shall know that I am Jehovah.

As thou best rejoiced over the inheritance of the house of Israel, because it was laid waste, so will I do to thee: thou shalt be laid waste, O mount Seir, and all Idumea: and they shall know that I am the Lord.

As thou didst rejoice at the inheritance of the house of Israel, because it was desolated, so will I do unto thee: thou shalt be a desolation, O mount Seir, and all Edom, the whole of it: and they shall know that I am Jehovah.

According to thy joy at the inheritance of the house of Israel because of desolation, So I do to thee, a desolation thou art, O mount Seir, and all Edom, all of it, And they have known that I am Jehovah!

As you did rejoice at the inheritance of the house of Israel, because it was desolate, so will I do to you: you shall be desolate, O mount Seir, and all Idumea, even all of it: and they shall know that I am the LORD.

You will become a waste, O Mount Seir, and all Edom, even all of it: and you will be certain that I am the Lord.

Just as you have rejoiced over the inheritance of the house of Israel, when it was laid waste, so will I act toward you. You will be laid waste, O mount Seir, with all of Idumea. And they shall know that I am the Lord."

So will I do unto thee - Others shall rejoice in thy downfall as thou hast rejoiced at their downfall.
This whole chapter strongly inculcates this maxim: Do as thou wouldst be done by; and what thou wouldst not have done to thee, do not to others. And from it we learn that every man may, in some sort, be said to make his own temporal good or evil; for as he does to others, God will take care to do to him, whether it be evil or good, weal or wo. Would you not be slandered or backbitten? Then do not slander nor backbite. Wouldst thou wish to live in peace? Then do not disturb the peace of others. Be merciful, and thou shalt obtain mercy.

As thou didst rejoice at the inheritance of the house of Israel, because it was desolate,.... So Edom rejoiced at the destruction of Jerusalem, Obadiah 1:12, and so the followers of the man of sin will rejoice at the slaying of the witnesses, Revelation 11:10, which is resented by the Lord, and therefore adds,
so will I do unto thee; make thee desolate, as is explained in the next clause:
thou shall be desolate, O Mount Seir, and all Idumea, even all of it; not that mount only, but all the land of Edom, called Idumea; the destruction shall be general, as it was, and irretrievable; and so not Rome only, but all the antichristian states, will be destroyed, when God comes forth in his wrath against them:
and they shall know that I am the Lord; the Lord God omniscient and omnipotent; who, having foretold all this, shall accomplish it.

(Obadiah 1:12, Obadiah 1:15).
The distinction between Israel and the heathen (as Edom) is: Israel has a covenant relation to God ensuring restoration after chastisement, so that the heathen's hope of getting possession of the elect people's inheritance must fail, and they themselves be made desolate (Ezekiel 36:1-15). The reason for the chastisement of Israel was Israel's sin and profanation of God's name (Ezekiel 36:16-21). God has good in store for Israel, for His own name's sake, to revive His people; first, by a spiritual renewal of their hearts, and, next, by an external restoration to prosperity (Ezekiel 36:22-33). The result is that the heathen shall be impressed with the power and goodness of God manifested so palpably towards the restored people (Ezekiel 36:34-38).