It is as high as heaven - That is, the knowledge of God; or the subject is as high as heaven. The idea is, that man is incompetent to examine, with accuracy, an object that is as far off as the heavens; and that as the knowledge of God must be of that character, it is vain for him to attempt to investigate it fully. There is an energy in the Hebrew which is lost in our common translation. The Hebrew is abrupt and very emphatic: “The heights of the heavens!” It is the language of one looking up with astonishment at the high heavens, and over-powered with the thought that the knowledge of God must be higher even than those distant skies. Who can hope to understand it? Who can be qualified to make the investigation? It is a matter of simple but sublime truth, that God must be higher than these heavens; and when we take into view the amazing distances of many of the heavenly bodies, as now known by the aid of modern astronomy, we may ask with deeper emphasis by far than Zophar did. “Can we, by searching, find out God?”
Deeper than hell - Hebrew “Than Sheol” - משׁאול meshe'ôl. The Septuagint renders this, “the heaven is high, what canst thou do? And there are things deeper than in Hades - βαθύτερα τῶν ἐν ᾃδου bathutera tōn en Hadou - what dost thou know?” On the meaning of the word Sheol, see Isaiah 5:14, note; Isaiah 14:9, note. It seems to have been supposed to be as deep as the heavens are high; and the idea here is, that it would be impossible for man to investigate a subject that was as profound as Sheol was deep. The idea is not that God was in Sheol, but that the subject was as profound as the abode of departed spirits was deep and remote. It is possible that the Psalmist may have had this passage in his eye in the similar expression, occurring in Psalms 139:
If I ascend into heaven, thou art there;
If I make my bed in hell, behold thou art there.