Is the threat of torment and Hellfire merely to frighten people away from sins, and that Allah gains nothing from their torment or worship?

This statement is false, due to the numerous Quranic verses in which Allah Almighty swears to the occurrence of what He has promised people regarding punishment or recompense, such as His saying: "By those [winds] that scatter, scattering, And those [clouds] that carry a heavy burden, And those [ships] that sail with ease, And those [angels] who distribute [orders] by command – Indeed, what you are promised is true. And indeed, the recompense is to occur." And His saying: "By the mount And a Book inscribed In parchment unrolled And by the frequented House And by the elevated ceiling And by the engulfed sea, Indeed, the punishment of your Lord will occur. There is no preventer of it." In addition, the Prophet, may Allah’s prayers and peace be upon him, saw many who were being punished in the Barzakh (definition) and the Hereafter.