He saw clearly both the disorder and incompleteness of human actions (compare the marginal reference), and also man's impotence to rectify them.

That which is crooked cannot be made straight - There are many apparent irregularities and anomalies in nature for which we cannot account; and there are many defects that cannot be supplied. This is the impression from a general view of nature; but the more we study and investigate its operations, the more we shall be convinced that all is a consecutive and well-ordered whole; and that in the chain of nature not one link is broken, deficient, or lost.

[That which is] (k) crooked cannot be made straight: and that which is lacking cannot be numbered.
(k) Man is not able by all his diligence to cause things to go other than they do: neither can he number the faults that are committed, much less remedy them.

That which is crooked cannot be made straight,.... By all the art and cunning, wisdom and knowledge of man, that he can attain unto; whatever he, in the vanity of his mind, may find fault with in the works of God, either of nature of providence, and which he may call crooked, it is not in his power to make them straight, or to mend them; see Ecclesiastes 7:13. There is something which, through sin, is crooked, in the hearts, in the nature, in the principles, ways and works, of men; which can never be made straight, corrected or amended, by all the natural wisdom and knowledge of men, which shows the insufficiency of it: the wisest philosophers among men, with all their parade of wit and learning, could never effect anything of this kind; this only is done by the Spirit and grace of God; see Isaiah 42:16;
and that which is wanting cannot be numbered; the deficiencies in human science are so many, that they cannot be reckoned up; and the defects in human nature can never be supplied or made up by natural knowledge and wisdom; and which are so numerous, as that they cannot be understood and counted. The Targum is,
"a man whose ways are perverse in this world, and dies in them, and does not return by repentance, he has no power of correcting himself after his death; and a man that fails from the law and the precepts in his life, after his death hath no power to be numbered with the righteous in paradise:''
to the same sense Jarchi's note and the Midrash.

Investigation (Ecclesiastes 1:13) into human ways is vain labor, for they are hopelessly "crooked" and "cannot be made straight" by it (Ecclesiastes 7:13). God, the chief good, alone can do this (Isaiah 40:4; Isaiah 45:2).
wanting-- (Daniel 5:27).
numbered--so as to make a complete number; so equivalent to "supplied" [MAURER]. Or, rather, man's state is utterly wanting; and that which is wholly defective cannot be numbered or calculated. The investigator thinks he can draw up, in accurate numbers, statistics of man's wants; but these, including the defects in the investigator's labor, are not partial, but total.

The judgment contained in the words, "vanity and a striving after the wind," is confirmed: "That which is crooked cannot become straight; and a deficit cannot be numerable," i.e., cannot be taken into account (thus Theod., after the Syro-Hex.), as if as much were present as is actually wanting; for, according to the proverb, "Where there is nothing, nothing further is to be counted." Hitzig thinks, by that which is crooked and wanting, according to Ecclesiastes 7:13, of the divine order of the world: that which is unjust in it, man cannot alter; its wants he cannot complete. But the preceding statement refers only to labour under the sun, and to philosophical research and observation directed thereto. This places before the eyes of the observer irregularities and wants, brings such irregularities and wants to his consciousness, - which are certainly partly brought about and destined by God, but for the most part are due to the transgressions of man himself, - and what avails the observer the discovery and investigation? - he has only lamentation over it, for with all his wisdom he can bring no help. Instead of לתקן (vid., under תקן), לתקן was to be expected. However, the old language also formed intransitive infinitives with transitive modification of the final vowels, e.g., יבשׁ, etc. (cf. ישׁון, Ecclesiastes 5:11).
Having now gained such a result in his investigation and research by means of wisdom, he reaches the conclusion that wisdom itself is nothing.

Crooked - All our knowledge serves only to discover our miseries, but is utterly insufficient to remove them; it cannot rectify those disorders which are either in our own hearts and lives, or in the men and things of the world. Wanting - In our knowledge. Or, counted out to us from the treasures of human learning. But what is wanting, will still be so. And that which is wanting in our own knowledge, is so much that it cannot be numbered. The more we know, the more we see of our own ignorance.