Tafsir of Az-Zumar 39:19

The original structure of the speech: "Is then one against whom the word of punishment has become justified, and you [attempt to] save him?" is a conditional sentence preceded by the interrogative hamza of denial, with the fa acting as the fa of the consequence (jaza'). The fa at the beginning is for conjunction with a deleted clause implied by the address. Its estimation is: "Are you the master of their affairs? So, is one against whom the punishment has become justified, you [attempt to] save him?"

The second hamza is the same as the first; it is repeated to emphasize the meaning of denial and improbability. The phrase "who is in the Fire" is placed in the position of the pronoun. According to this view, the verse is a single sentence.

Another perspective: The verse consists of two sentences: "Is then one against whom the punishment has become justified, you [attempt to] rescue him? Are you [able to] save one who is in the Fire?" The deletion of "you [attempt to] rescue him" is permissible because "Are you [able to] save" implies it.

Their entitlement to punishment while in this world is treated as equivalent to their entry into the Fire, to the extent that the Prophet’s (peace be upon him) exertion and exhaustion of himself in calling them to faith is treated as equivalent to saving them from the Fire.

His saying, "Are you [able to] save," conveys that Allah Almighty is the only One capable of saving from the Fire; no one else is capable of that. Just as you are unable to save one who has entered the Fire from the Fire, you are unable to save him from the state he is in—the entitlement to punishment—by producing faith within him.