I’d like to begin by stating that the Book of Job was inspired by the Holy Spirit. As such, 2 Timothy 3:16, 17 certainly applies: “All scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness: That the man of God may be perfect, thoroughly furnished unto all good works”.  The word “inspiration” in this verse means “God breathed,” so we know that what is written there is all true, and I believe that what Job knew of God must have come to him as a direct revelation from God, since as you say, there were as yet no Scriptures to teach Job. In John 1:1, we read “In the beginning was the Word, and the Word was with God, and the Word was God”. Thus, the Word of God existed before the written Word, and so the early patriarchs had to learn the will of God through some type of divine revelation.

Jewish tradition places Moses as the author of this book, the words likely being passed down through the years via oral tradition which tends to be extremely accurate. Many scholars believe that this is the oldest book in the Bible, and that the life of Job pre-dates that of Abraham. MacDonald in his Bible Commentary, in the introduction to the Book of Job, states: “Although the author of the book of Job is unknown, there is no question as to its inspiration or historical accuracy. The Apostle Paul quotes from Job 5:13 in 1 Corinthians 3:19: “He catches the wise in their own craftiness.” He is also mentioned in James 5:11: “You have heard of the perseverance of Job and seen the end intended by the Lord-that the Lord is very compassionate and merciful”.

Personally, I believe that the Book of Job pre-dates the rest of the Scriptures, and I believe this to be so because in the entire book, we hear nothing of Abraham, the children of Israel, nor of the law of Moses. So, if Job had no Scriptures to consult to give him such a strong faith and knowledge of God, I think I can say without reservation that the LORD must have directly revealed to Job the vast knowledge of His ways and will. If you ask me how God accomplished this precisely, I would be unable to answer with confidence. However, somehow, the divine knowledge was conferred to Job, whether by visions, dreams, or angelic announcements. Scripture has many examples of how God made known His will to those with a heart for God through means other than the written Word. I will therefore now try to present some Scriptural warrants and examples of what I am talking about.

To begin with, God was very aware of Job among all the people on the earth, and was pleased with his faith and obedience as we see in Job 1:8: “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?” Additionally, Job appears to have been a “priest” in his own home in the years preceding the events of this book, as we read in Job 1:5: “And it was so, when the days of their feasting were gone about, that Job sent and sanctified them, and rose up early in the morning, and offered burnt offerings according to the number of them all: for Job said, It may be that my sons have sinned, and cursed God in their hearts. Thus did Job continually”. Such information could only have come from God through some type of revelation. So, God made His will known to Job early on, and Job faithfully responded.

For additional examples of how God communicated divine wisdom with men in the days before the Scriptures, consider the cases of Noah, Job himself, Abraham, and Daniel. Well before the written Word, Noah appears to have been a priest for his family (Genesis 8:20-he built an alter), and God spoke directly to him in Genesis 6:8,9;6:13-22. Similarly, we read from Job 38 onward that God spoke directly to Job out of the whirlwind, so here is an example of God directly communicating with man. In Genesis 12:1-7, we see that God spoke to Abram who lived in Ur of the Chaldees (present day Iraq). Abram (Abraham) had no Scriptures either but heard from God directly as to what he was to do, and Abram followed God’s direction to the letter and became the patriarch of the Jewish nation. Daniel received a visit from an angel of the Lord, revealing to him all about the previously unwritten mysteries of the end times (Daniel 9:21,22, and to the end of chapter 12). You might also recall that God spoke to Moses directly before the Scriptures were penned out (Exodus 3:4, and throughout Exodus 3-40). Then, of course, there are the major and the minor prophets, each of whom received directly the Word of the Lord. In the New Testament, before the NT Scriptures were written, we see that Saul of Tarsus in Acts 9:4-6, and Peter and Cornelius in Acts 10:1-33 received direct communications from the Lord.  

So, in short, I believe that where there are no Scriptures to go on, God relates His Word and will to those who are open to His leading. God knew that Job’s heart was open to Him, and He somehow communicated to him how that he should walk with God, shunning evil, making sacrifices to the Lord, but more than that, how to walk in faith and obedience to the sovereign will of God, in a way that was pleasing to the Lord. Job’s faith and understanding were expanded by the tough experiences that God allowed him to go through. Thus, in the end, Job learned that God is good and gracious, and that His sovereign will is not to be questioned by mortal men, but rather to be accepted in faith.  (SF)  (530.5)