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 Ps. 139:
If I ascend into heaven, thou art there;
If I make my bed in hell, behold thou art there.

It is as high as heaven - High as the heavens, what canst thou work? Deep below sheol, (the invisible world), what canst thou know? Long beyond the earth, and broad beyond the sea, is its measure. These are instances in the immensity of created things, and all out of the reach of human power and knowledge; and if these things are so, how incomprehensible must he be, who designed, created, preserves, and governs the whole!
We find the same thought in Milton: -
"These are thy glorious works, Parent of good!
Almighty! Thine this universal frame:
How wondrous fair! Thyself how wondrous then!"

[It is] as high as heaven; what canst thou do? (d) deeper than hell; what canst thou know?
(d) That is, this perfection of God, and if man is not able to comprehend the height of the heavens, the depth of the earth, the breadth of the sea, which are but creatures, how can he attain to the perfection of the creator.

It is as high as heaven; what canst thou do?.... Or, "is higher than the heavens" (i); either the wisdom of God and the secrets of it; the perfection of his wisdom, by which he has made the heavens; or evangelical wisdom, hid in his heart, and which the highest of creatures, the angels, come at the knowledge of only by revelation; and therefore, what can man do to find it out, unless God reveals it? or wisdom displayed in dark providences, which can never be accounted for until the judgments of God are made manifest: or else, "he that is God", as the Vulgate Latin version, is "higher than the heavens"; the heaven is his throne on which he sits, and therefore he must be higher than that; the heavens, and heaven of heavens, cannot contain him; he fills up the infinite space beyond them; how is it possible therefore to find him out, to comprehend him?
deeper than hell; what canst thou know? meaning, neither the grave nor the place of the damned, for both which "Sheol" is sometimes used, but the centre or lowest part of the earth; there is a depth in God, in his essence, in his thoughts, in his wisdom, displayed in nature, providence, and grace, that is unfathomable; we can know nothing of it but what he is pleased to make known; see Psalm 92:5; the Targum of the verse is,"in the height of heaven, what canst thou do? in the law, which is deeper than hell, what canst thou know?''
(i) "altior est altissimis coelis", Junius & Tremellius.

It--the "wisdom" of God (Job 11:6). The abruptness of the Hebrew is forcible: "The heights of heaven! What canst thou do" (as to attaining to them with thy gaze, Psalm 139:8)?
know--namely, of His perfections.