Adam Clarke on Isaiah 29:2

There shall be heaviness and sorrow "There shall be continual mourning and sorrow" - Instead of your present joy and festivity.

And it shall be unto me as Ariel "And it shall be unto me as the hearth of the great altar" - That is, it shall be the seat of the fire of God; which shall issue from thence to consume his enemies. See note on Isa 29:1 (note). Or, perhaps, all on flame; as it was when taken by the Chaldeans; or covered with carcasses and blood, as when taken by the Romans: an intimation of which more distant events, though not immediate subjects of the prophecy, may perhaps be given in this obscure passage.