Commentary for Job 42:3

Who is this who concealed and covered the counsel and the wonders of the Holy One, blessed be He, without knowledge? I knew that everything is in Your hand to do, and so I related some of Your mighty deeds as were in my heart; as I knew [them].

In his reply to God, Job paraphrases the very challenge God had made to him at the beginning of His oration (Job 38:2). It was because he did not want God's design to remain just a matter of faith, shrouded in mystery and uncertainty, that he had initiated the debate.
Responding to God in His own words (Job 38:3), Job explains that just as He had called for answers from Job, so Job had been seeking answers from God. Job's contention had been that rational answers should be given to the great issues raised by ethical monotheism; they should not be just matters of faith. And if man is unable to find these rational answers unaided, God ought to provide them.

but I did not understand But I did not understand so much, as You informed me, for many wonders are hidden and concealed from me, which I do not know.