It is the entire premise of the story. It’s literally the only way Satan could “win” his bet with God.
“Then Satan answered the LORD, and said, Doth Job fear God for nought? 1:10 Hast not thou made an hedge about him, and about his house, and about all that he hath on every side? thou hast blessed the work of his hands, and his substance is increased in the land. 1:11 But put forth thine hand now, and touch all that he hath, and he will curse thee to thy face”
God proceeded to give Satan permission to put forth them hands on Job’s family, and wealth, and health to prove he was right and Satan was wrong. Job would not curse God (say mean things).
I suppose it’s possible Job would be rewarded either way, but, either way, his kids were all slaughtered. And taking the Lord’s name in vain is a sin. Presumably even if the Lord tries to make you do it as a test.
Again, I’m not saying anything that isn’t written in plain text.
The reward for his loyalty included replacing his slain kids with some new kids.
Apparently, Job was supposed to be happy because his new daughters were beautiful (I guess more beautiful than his 3 original daughters?).
“So the LORD blessed the latter end of Job more than his beginning: for he had fourteen thousand sheep, and six thousand camels, and a thousand yoke of oxen, and a thousand she asses. 42:13 He had also seven sons and three daughters. 42:14 And he called the name of the first, Jemima; and the name of the second, Kezia; and the name of the third, Keren-happuch. 42:15 And in all the land were no women found so fair as the daughters of Job: and their father gave them inheritance among their brethren”
People can certainly be cool with this, and find spiritual meaning or whatever, but I can’t see how anything I’ve said is even debatable.