نَارُ ٱللَّهِ ٱلْمُوقَدَةُ
The answer to the question of the fifth verse begins here. The sentence is a nominal one; its subject is an implied hiya, or else it is directly a predicate clause: "[It is] the kindled fire of God."
The fire has been annexed to the name of God. This choice is worth dwelling on, because the Qurʾān does not use this construct everywhere it speaks of the fire of Hell.
One — magnification and intensification. In Arabic, the annexing of a thing to God conveys its greatness. The expression "the fire of God" says that this fire is of a different order from the fires that are known.
Two — to set it apart from the fire of this world. When "fire" is said, the one addressed will think of the thing he knows. The construct cuts that thought off.
There is a third explanation, and I add it as my own reading: all through the sūra the question of ownership was being treated. The man gathered the wealth, counted it, counted it his own, expected permanence from it. That the fire is named by the name of its owner is a sentence placed at the end of this series of ownership. To whom the wealth belonged was in dispute; to whom the fire belongs is not.
Al-mūqada is the passive participle of Form IV: kindled, set alight. That is, not a fire that burns of itself but a fire that is lit. The fire has one who lights it.
It is instructive to set the two verses side by side: the fire man kindles is put out; of the fire God kindles no such thing is said.
And the connection with al-Baqara 2/24 says one thing more: that the fuel is man himself. The man was gathering wealth; in the end he becomes fuel.