SB 6.9.50

svayaṁ niḥśreyasaṁ vidvān
 na vakty ajñāya karma hi
na rāti rogiṇo ’pathyaṁ
 vāñchato ’pi bhiṣaktamaḥ
Word for word: 
svayam — personally; niḥśreyasam — the supreme goal of life, namely the means of obtaining ecstatic love for the Supreme Personality of Godhead; vit-vān — one who is accomplished in devotional service; na — not; vakti — teaches; ajñāya — unto a foolish person not conversant with the ultimate goal of life; karma — fruitive activities; hi — indeed; na — not; rāti — administers; rogiṇaḥ — unto the patient; apathyam — something unconsumable; vāñchataḥ — desiring; api — although; bhiṣak-tamaḥ — an experienced physician.
Translation: 
A pure devotee who is fully accomplished in the science of devotional service will never instruct a foolish person to engage in fruitive activities for material enjoyment, not to speak of helping him in such activities. Such a devotee is like an experienced physician, who never encourages a patient to eat food injurious to his health, even if the patient desires it.
Purport: 

Here is the difference between the benedictions awarded by the demigods and those awarded by the Supreme Personality of Godhead, Viṣṇu. Devotees of the demigods ask for benedictions simply for sense gratification, and therefore they have been described in Bhagavad-gītā (7.20) as bereft of intelligence.

kāmais tais tair hṛta-jñānāḥ
 prapadyante ’nya-devatāḥ
taṁ taṁ niyamam āsthāya
 prakṛtyā niyatāḥ svayā

“Those whose minds are distorted by material desires surrender unto demigods and follow the particular rules and regulations of worship according to their own natures.”

Conditioned souls are generally bereft of intelligence because of profound desires for sense gratification. They do not know what benedictions to ask. Therefore nondevotees are advised in the śāstras to worship various demigods to achieve material benefits. For example, if one wants a beautiful wife, he is advised to worship Umā, or the goddess Durgā. If one wants to be cured of a disease, he is advised to worship the sun-god. All requests for benedictions from the demigods, however, are due to material lust. The benedictions will be finished at the end of the cosmic manifestation, along with those who bestow them. If one approaches Lord Viṣṇu for benedictions, the Lord will give him a benediction that will help him return home, back to Godhead. This is also confirmed by the Lord Himself in Bhagavad-gītā (10.10):

teṣāṁ satata-yuktānāṁ
 bhajatāṁ prīti-pūrvakam
dadāmi buddhi-yogaṁ taṁ
 yena mām upayānti te

Lord Viṣṇu, or Lord Kṛṣṇa, instructs a devotee who constantly engages in His service how to approach Him at the end of his material body. The Lord says in Bhagavad-gītā (4.9):

janma karma ca me divyam
 evaṁ yo vetti tattvataḥ
tyaktvā dehaṁ punar janma
 naiti mām eti so ’rjuna

“One who knows the transcendental nature of My appearance and activities, does not, upon leaving the body, take his birth again in this material world, but attains My eternal abode, O Arjuna.” This is the benediction of Lord Viṣṇu, Kṛṣṇa. After giving up his body, a devotee returns home, back to Godhead.

A devotee may foolishly ask for material benedictions, but Lord Kṛṣṇa does not give him such benedictions, despite the devotee’s prayers. Therefore people who are very attached to material life do not generally become devotees of Kṛṣṇa or Viṣṇu. Instead they become devotees of the demigods (kāmais tais tair hṛta jñānāḥ prapadyante ’nya-devatāḥ). The benedictions of the demigods, however, are condemned in Bhagavad-gītā. Antavat tu phalaṁ teṣāṁ tad bhavaty alpa-medhasām: “Men of small intelligence worship the demigods, and their fruits are limited and temporary.” A non-Vaiṣṇava, one who is not engaged in the service of the Supreme Personality of Godhead, is considered a fool with a small quantity of brain substance.