One major question that is addressed in Job is why do the faithful suffer, and in the context, why was Job suffering. The answer to this is given in the course of the whole book and narrative. The overall perspective is really an introduction to the sacrifice of Christ, as a representative not a substitute.
The first chapter of Job tells us why Job was suffering. What follows until chapters 38-41 are:
1. The condemnation of Job as suffering because he had committed egregious sins. (Judgmental people who think they know it all and use God as their backup in sitting as judge.)
2. Job's defense of himself to his friends.
3. Job's lament that he could not defend himself to God and get an answer from him.
4. Job's desperation at not being able to understand why he was suffering.
In chapters 38-41 God speaks to Job telling of his greatness and sovereignty over all creation, and the arrogance and smallness of Job.
After hearing this, in verse 42:1-6 Job breaks. God became more to him than simple knowledge. He had been blind, but now he saw.
As an aside: That very same thing happened to me early in my Christian walk, reading God's voice in 38-41 and coming to 42. I had been in those blessed days God often gives to the new convert, of having all their prayers answered on the spot as a way of assuring them that yes, he is real, yes he hears and sees and knows. But I had been praying for something (rain to save my vegetable garden, a simple but very necessary thing, and that is how simple and childlike my faith was at the time) for weeks. I had been talking back to God in frustration and anger. Every night there was thunder and streaks of rain all around me, but no rain fell on my land. Even that night there was the distant rumble of thunder. I was in awe as I read those chapters starting in 38, stunned, and broke as Job had when I read his words of 42. I wept (and I am not one who cries easily) and asked forgiveness for my anger at him. And it began to rain. That was a wake up call. Time to begin growing up.
In 42:7 God rebukes Job's friends.
After the Lord had spoken these words to Job, the Lord said to Eliphaz the Temanite: "My anger burns against you and against your two friends, for you have not spoken of me what is right, as my servant Job has.
There is no representation or substitution of Christ in the book of Job as a perspective. Someone has read Job and looked for application but not meaning (and probably a presupposed application) and misapplied the application that is in the book----and you have believed them.
No. Sin is the transgression of the Law. I object to the term "sinful nature" being applied to Christ, without understanding that He came in the likeness of sin's flesh.
It is you who have said that Jesus had a sinful nature. Flesh is in and of itself not sinful. That is a Gnostic belief. God created flesh. Sinful flesh does not mean flesh is sinful and sin does not have flesh. It means we have flesh and we sin.