SB 11.11.19

gāṁ dugdha-dohām asatīṁ ca bhāryāṁ
 dehaṁ parādhīnam asat-prajāṁ ca
vittaṁ tv atīrthī-kṛtam aṅga vācaṁ
 hīnāṁ mayā rakṣati duḥkha-duḥkhī
Synonyms: 
gām — a cow; dugdha — whose milk; dohām — already taken; asatīm — unchaste; ca — also; bhāryām — a wife; deham — a body; para — upon others; adhīnam — always dependent; asat — useless; prajām — children; ca — also; vittam — wealth; tu — but; atīrthī-kṛtam — not given to the proper recipient; aṅga — O Uddhava; vācam — Vedic knowledge; hīnām — devoid; mayā — of knowledge of Me; rakṣati — he takes care of; duḥkha-duḥkhī — he who suffers one misery after another.
Translation: 
My dear Uddhava, that man is certainly most miserable who takes care of a cow that gives no milk, an unchaste wife, a body totally dependent on others, useless children or wealth not utilized for the right purpose. Similarly, one who studies Vedic knowledge devoid of My glories is also most miserable.
Purport: 

A human being is actually learned or expert when he understands that all material objects perceived through the various senses are expansions of the Supreme Personality of Godhead and that nothing exists without the support of the Supreme Lord. In this verse, through various examples, it is concluded that the power of speech is useless if not engaged for the Supreme Lord. According to Śrīla Viśvanātha Cakravartī Ṭhākura, this verse implies that all of the functions of the various senses are useless if they are not engaged in the glorification of God. Indeed, the avadhūta brāhmaṇa previously stated to King Yadu that if the tongue is not controlled, one’s entire program of sense control is a failure. One cannot control the tongue unless he vibrates the glories of the Lord.

The example of the milkless cow is significant. A gentleman never kills a cow, and therefore when a cow becomes sterile and no longer gives milk, one must engage in the laborious task of protecting her, since no one will purchase a useless cow. For some time, the greedy owner of a sterile cow may continue thinking, “I have already invested so much money in taking care of this cow, and certainly in the near future she will again become pregnant and give milk.” But when this hope is proven futile, he becomes neglectful and indifferent to the health and safety of the animal. Because of such sinful neglect, he must suffer in the next life, after having already suffered because of the sterile cow in the present life.

Similarly, although a man may discover that his wife is neither chaste nor affectionate, he may be so eager to get children that he goes on taking care of such a useless wife, thinking, “I will teach my wife the religious duties of a chaste woman. By hearing historical examples of great women surely her heart will change, and she will become a wonderful wife to me.” Unfortunately, the unchaste wife in many cases does not change and also gives a man many useless children who are just as foolish and irreligious as she. Such children never give any happiness to the father, yet the father tediously labors to take care of them.

Also, one who has accumulated wealth by the mercy of God must be vigilant to give in charity to the right person and for the right cause. If such a right person or cause appears and one hesitates and selfishly does not give in charity, one loses his reputation, and in the next life he will be poverty-stricken. One who fails to give properly in charity spends his life anxiously protecting his wealth, which ultimately brings him no fame or happiness.

The previous examples are given to illustrate the uselessness of laboriously studying Vedic knowledge that does not glorify the Supreme Personality of Godhead. Śrīla Jīva Gosvāmī comments that the spiritual vibration of the Vedas is meant to bring one to the lotus feet of the Supreme Lord, Kṛṣṇa. Many processes for achieving the Supreme Truth are recommended in the Upaniṣads and other Vedic literatures, but because of their innumerable and seemingly contradictory explanations, commentaries and injunctions, one cannot achieve the Absolute Truth, the Personality of Godhead, merely by reading such literature. If, however, one understands Śrī Kṛṣṇa to be the ultimate cause of all causes and reads the Upaniṣads and other Vedic literature as glorification of the Supreme Lord, then one can actually become fixed at the Lord’s lotus feet. For example, His Divine Grace Śrīla Prabhupāda translated and commented upon Śrī Īśopaniṣad in such a way that it brings the reader closer to the Supreme Personality of Godhead. Undoubtedly, the lotus feet of Lord Kṛṣṇa are the only reliable boat by which to cross the turbulent ocean of material existence. Even Lord Brahmā has stated in the Tenth Canto of Śrīmad-Bhāgavatam that if one gives up the auspicious path of bhakti and takes to the fruitless labor of Vedic speculation, one is just like a fool who beats empty husks in hopes of getting rice. Śrīla Jīva Gosvāmī recommends that one completely ignore dry Vedic speculation because it does not bring one to the point of devotional service to the Absolute Truth, Lord Śrī Kṛṣṇa.