Even though he should die without receiving justice, Job hopes that a witness in heaven will step forward to take his side and to declare him innocent. Since none of his friends will do it, he hopes for a heavenly figure to take his case.
Job seems to have in mind the story of The elder son of Adam and Eve, Cain murdered his brother Abel. More and The second son of Adam and Eve who was murdered by Cain. More. Cain killed Abel where there were no witnesses. But God heard Abel’s blood crying out from the ground, and God responded to bring justice (Genesis 4:10-12). Since there were no humans to testify on Abel’s behalf, justice was only possible if God intervened. Similarly, Job has received no words of comfort and affirmation from his friends. His only chance is for some divine action to hear his cry and take his case.
Who does Job have in mind when he speaks of a “witness”? Clearly, it is not another human. So, who in heaven has the proximity and clout to argue with God on Job’s behalf? Is it some angel or other heavenly being? Christians tend to see Christ in passages like this. At least, the function that Job wants from the witness is similar to the way they hope that Christ makes the case for their justification before God. Perhaps Job is appealing to one side of God’s nature against the other side. He wants the good God who made him and loved and sustained him to appeal to the harsh side of a demanding God. He wants God’s Mercy is a term used to describe leniency or compassion. God's mercy is frequently referred to or invoked in both the Old and New Testaments. More to prevail over God’s demands for obedience. He wants God, who is both merciful and just, to lean in the direction of mercy.