It's not that it was hidden. It's that it's not really a legitimate interpretation.
Job didn't believe that the Messiah was a mere man. Job's Redeemer
Job’s Surge of Faith
First, the suffering sage longed to make a permanent declaration of his innocence (i.e., his current affliction is undeserved). Oh, that his protest might be written in a book; better yet, let it be carved in stone (the depressions of which would be filled with lead—real permanence!). Thus, when vindication eventually comes, his integrity would be established.
Then, Job expressed deep confidence relative to the existence of his Redeemer-God. “I know,” he declared, “that my Redeemer lives.” The Hebrew term denotes knowledge of a personal, experiential nature. In the original text, the emphatic position of the pronoun “I” indicates that Job had a settled conviction regarding his Redeemer (Smick 1988, 942).
The word “Redeemer” is of great significance. The term is go’el which, along with its derivatives, is found about 118 times in the Old Testament. The basic meaning of the word is “to do the part of a kinsman,” and thus “to redeem” one’s kin from difficulty or danger (Harris 1980, 144). The Redeemer could: avenge a slain kinsman (Numbers 35:19-27); marry a deceased relative’s childless widow (Ruth 4:10); purchase a loved one out of slavery (Leviticus 25:47-55); or buy back a kinsman’s property that had passed from the family (Leviticus 25:23-25). The word is also used of God, as one who vindicates and redeems his people (Isaiah 43:1-3).