The "Satan" of Job is not the "Satanas" of the New Testament. The individual in Job is a "son of God" carrying out activities under Yahweh's permission.
The purpose of the Book of Job was to create an explanation for the sorry state of "God's people", laying the blame away from Yahweh. Their very recent (6th century BCE) experiences coupled with their very recent surge of Monotheism created the issue of Theodicy, which the Book of Job addresses in the concepts of their day.
I suspect it is likely there is a soteriological intent with the story of Satan's temptation of Christ. I will research further but my initial thoughts include:
The intention of the writers (40 to 60 years after the setting of the story) might simply be wanting to show the authority of their ancient written documents.
Secondly, they might be saying that if you are tempted in these ways, this is how you are to respond.
I am probably way off the mark, but it is at least a starting point.
In other words, rather than asking only what did they write, I want to know why they wrote.
If someone offered you the world (winning the lottery; becoming POTUS; etc.) how would you respond? Is that what these writers were posing? And then setting up Christ as the model respondent.
Just assuming at this stage.