There's several important lessons within Job.
Job 2:2-6
2 And the LORD said unto Satan, From whence comest thou? And Satan answered the LORD, and said, From going to and fro in the earth, and from walking up and down in it.
3 And the LORD said unto Satan, Hast thou considered My servant Job, that there is none like him in the earth, a perfect and an upright man, one that feareth God, and escheweth evil? and still he holdeth fast his integrity, although thou movedst Me against him, to destroy him without cause.
4 And Satan answered the LORD, and said, Skin for skin, yea, all that a man hath will he give for his life.
5 But put forth Thine hand now, and touch his bone and his flesh, and he will curse Thee to thy face.
6 And the LORD said unto Satan, Behold, he is in thine hand; but save his life.
(KJV)
With the above, God is actually bragging on Job's faithfulness when He speaks to Satan. Satan then tempts God to touch Job betting that Job will curse God eventually through trials and temptations. That's something very deep to consider, because it's like God was intending to prove something to Satan by seeming to accept a challenge (which really was no challenge to God), and He obviously wanted us to know about it since this was before Job's testing had begun.
Job 2:9-10
9 Then said his wife unto him, Dost thou still retain thine integrity? curse God, and die.
10 But he said unto her, Thou speakest as one of the foolish women speaketh. What? shall we receive good at the hand of God, and shall we not receive evil? In all this did not Job sin with his lips.
(KJV)
Job's own wife spoke as if she believed Job was guilty of some offense which had caused his trials.
Job 4:6-9
6 Is not this thy fear, thy confidence, thy hope, and the uprightness of thy ways?
7 Remember, I pray thee, who ever perished, being innocent? or where were the righteous cut off?
8 Even as I have seen, they that plow iniquity, and sow wickedness, reap the same.
9 By the blast of God they perish, and by the breath of his nostrils are they consumed.
(KJV)
Job's three friends in the above also believed Job had done something wrong to deserve his trials. Yet they couldn't prove it.
Job 32:1-3
1 So these three men ceased to answer Job, because he was righteous in his own eyes.
2 Then was kindled the wrath of Elihu the son of Barachel the Buzite, of the kindred of Ram: against Job was his wrath kindled, because he justified himself rather than God.
3 Also against his three friends was his wrath kindled, because they had found no answer, and yet had condemned Job.
(KJV)
A fourth spoke, Elihu, condemning Job's three friends because they condemned Job without cause, only assuming he was guilty of something to deserve such a trial.
Job petitioned God for the cause of his trials, showing Job thought to retain his own sense of righteousness, asking God to show him what it was he had done wrong. Job tried to retain his guiltlessness even while admitting God's Authority and Power over all things.
Job 40:6-8
6 Then answered the LORD unto Job out of the whirlwind, and said,
7 Gird up thy loins now like a man: I will demand of thee, and declare thou unto me.
8 Wilt thou also disannul my judgment? wilt thou condemn Me, that thou mayest be righteous?
(KJV)
Satan's testing upon Job wasn't originally about whether or not Job was a sinner, for all born in the flesh except The Christ have sinned, including Job. What God had bragged to Satan about was in regard to Job's original faithfulness to God. God's later rebuke to Job was because of Job holding to his own sense of righteousness and judgment of having done nothing wrong to deserve his trial.
In reality, Job truly had not done anything wrong to bring Satan's trial. The trial was a matter between God and Satan. Still doesn't mean Job was without sin.
Job 42:7-13
7 And it was so, that after the LORD had spoken these words unto Job, the LORD said to Eliphaz the Temanite, My wrath is kindled against thee, and against thy two friends: for ye have not spoken of Me the thing that is right, as My servant Job hath.
8 Therefore take unto you now seven bullocks and seven rams, and go to My servant Job, and offer up for yourselves a burnt offering; and My servant Job shall pray for you: for him will I accept: lest I deal with you after your folly, in that ye have not spoken of Me the thing which is right, like My servant Job.
9 So Eliphaz the Temanite and Bildad the Shuhite and Zophar the Naamathite went, and did according as the LORD commanded them: the LORD also accepted Job.
10 And the LORD turned the captivity of Job, when he prayed for his friends: also the LORD gave Job twice as much as he had before.
11 Then came there unto him all his brethren, and all his sisters, and all they that had been of his acquaintance before, and did eat bread with him in his house: and they bemoaned him, and comforted him over all the evil that the LORD had brought upon him: every man also gave him a piece of money, and every one an earring of gold.
12 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.
13 He had also seven sons and three daughters.
(KJV)
When it was all over, Job received a double-portion to make up for all that he had lost, which is a sign of a chosen elect servant of God. The lesson I see with that is, with those of God's servants which He already... owns... He will use and move them how He sees fit, and they will not be forgotten by Him.