Do you know it, because you were born then? or because the number of your days is great?
All Commentaries on Job 38:21 Go To Job 38
Gregory The Dialogist
AD 604
35. As if He were openly saying, What wonder if thou understandest not thine end, since thou dost not comprehend thy beginning? And since thou knowest not with what beginning thou camest hither, what wonder, if thou canst not tell with what end thou art taken away? If therefore it was My work to bring thee forward from secresy to sight at thy beginning, it will be Mine also to bring thee back from sight to secresy. Why complainest thou aught of the dispensation of thy life, who, ignorant of thyself, art supported by the hand of thy Creator? Thou oughtest therefore to boast thyself the less in what thou dost, the more thou art confined within the bosom of eternity, and knowest not either in what order thou earnest hither, nor when, or how thou art taken hence.
36. But these words can yet be understood in another sense also; Didst thou know then that thou wast about to be born, and didst thou know the number of thy days? Thou understandest, As I, Who knew that I was about to be born, because, even before the birth of My Manhood, I always existed substantially in the Godhead. For men begin then to exist, when they are born in the womb of their mothers. For even the very conception is called nativity, according to that which is written, That which is born in her is of the Holy Ghost. [Matt. 1, 20] And they therefore know not that they are about to be born, because they do not exist, before they are created. But God, Who ever existed without beginning, foresaw this of Himself, that He assumed a beginning in the womb of the Virgin; and because He foreknew, He ordained it; and because He ordained, He doubtless endured nothing in human form, except of His own free will. Let man then, who could not foresee his own birth, be reproved for complaining of his scourges, if even He, Who foresaw and ordained His own birth, prepared Himself for scourges amongst men.