In Job, Satan was convinced Job's love for God was only because of reward. and if that were taken away he'd stop loving God.
So God, to prove Satan is wrong about this, allowed Satan to torment Job to test his faith. In the end, God was right.
Or something like that, right?
You have to fit this scenario into the big picture which began in Eden.
Why did satan challenge Job's integrity in the first place? He had already managed to deceive the first woman into disobeying the only command that carried the death penalty. But he was not actually targeting the woman, his real target was the man. Rom 5:12 identifies the man as the one through whom sin entered the world and spread to their children.
The woman was deceived, but the man was not. He wilfully and deliberately sided with his disobedient wife.
The point of getting humans to reject their Creator in the first place, was to make himself into their substitute god. He gave himself away when he told the woman she would "be like God" if she disobeyed his command, when that was really his desire all along. He also tried to get Jesus to do an act of worship to him by offering him something that would have tempted himself, so he isn't exactly subtle in letting us know his ambitions.
By zeroing in on a man of extraordinary faith like Job, and questioning his motive in serving his God 'like no other' human at the time, satan was trying to minimise the reasons for human faith....he claimed it was all selfish. Again he was accusing humans of being just like he is. He told God that if everything he valued was taken away, that Job would curse God to his face.
The only way to prove satan was a liar was to allow him to try his best to undermine Job's faith with tragedy and loss.
It didn't work, just as God knew it wouldn't. But satan was not satisfied......he didn't believe that the test had gone far enough. So he demanded that Job be afflicted personally with something that was painful and life threatening....and then he would curse God and abandon his worship. Again, the devil failed. He even provided men who implied that he must have done something very seriously wrong in order for God to be punishing him like that. In alwverything that he endured, even after his grieving wife told him to "curse God and die"....he still kept his integrity. What a man!
Paul's words in 1 Cor 10:13 tell us why God allowed this test....
"No temptation has come upon you except what is common to men. But God is faithful, and he will not let you be tempted beyond what you can bear, but along with the temptation he will also make the way out so that you may be able to endure it."
God knew that Job would remain faithful no matter what the devil did, and he kept a close eye on him as he allowed the devil's temptation to go so far and no further. It was God who drew the line in the sand in determining the limit of Job's endurance. And in the end, Job was rewarded for his faithfulness.
But Satan is known throughout the Bible as a trickster on the highest level.
So what if Satan already knew God would win. But pretended he didn't so this bet would actually be at play. Not to make Job stop loving God, but only so he had an excuse to let God torment him?
If you know what the devil is up to, you will be able to see in his words that it was all mankind that was under test here. In Job ch 2 :3-5 it says....
"And Jehovah said to Satan: “Have you taken note of my servant Job? There is no one like him on the earth. He is an upright man of integrity, fearing God and shunning what is bad. He is still holding firmly to his integrity, even though you try to incite me against him to destroy him for no reason.” But Satan answered Jehovah: “Skin for skin. A man will give everything that he has for his life. But, for a change, stretch out your hand and strike his bone and flesh, and he will surely curse you to your very face.”
Notice it says "A man will give everything that he has for his life" he didn't say Job would give everything, but a man...meaning all men. Satan was taunting God about all of us. (Prov 27:11)
It wasn't God who brought the calamity on Job......he only permitted it. Not many people take note of the end of the story....."After Job had prayed for his companions, Jehovah removed Job’s tribulation and restored his prosperity. Jehovah gave him double what he had before. 11 All his brothers and sisters and all his former friends came to him and ate a meal with him in his house. They sympathized with him and comforted him over all the calamity that Jehovah had allowed to come upon him. Each of them gave him a piece of money and a gold ring. 12 So Jehovah blessed the last part of Job’s life more than the beginning.......He also came to have seven more sons and three more daughters......After this Job lived for 140 years, and he saw his children and his grandchildren—four generations. Finally Job died, after a long and satisfying life." (Job 42:10-17)
Job believed in the resurrection of the dead......so just think......he will be reunited with all his children in the "new earth" under the rulership of Messiah's Kingdom....all 20 of them.
In this beautiful place, there will be no memory of the bad times....only the good times to come. (Isa 65:17; 2 Pet 3:13) 
