Adam Clarke on Job 42:8

Take - seven bullocks and seven rams - From this it appears that Job was considered a priest, not only in his own family but also for others. For his children he offered burnt-offerings, Job 1:5; and now he is to make the same kind of offerings, accompanied with intercession, in behalf of his three friends. This is a full proof of the innocence and integrity of Job: a more decided one could not be given, that the accusations of his friends, and their bitter speeches, were as untrue as they were malevolent. God thus clears his character, and confounds their devices.