Shukracharya being Bali’s spiritual master warned him not to give or promise anything to the dwarf Brahmana as He was none other than the Supreme Personality of Godhead, Hari who has accepted Kashyapa Muni as His father and Aditi as His mother, has come here to fulfill the interests of the demigods.
Shukracharya said Bali's promise will bring great harm to the demons. He again advised that he has come here to take away all his land, wealth, beauty, power, fame and education. After taking everything, He will deliver it to Indra, who is the king’s enemy.
This is the mentality of a Brahmana priest like Shukracharya who is only interested in material profit or personal gain and was concerned that his remuneration from the king would be in stake when the king loses everything.
But Bali Maharaj being a Vaishnava was interested only in satisfying the Supreme Personality of Godhead.
Shukracharya again warned "You have promised three steps, But with only two steps, all your possessions will be finished. How then will you give Him a place for His third step?"
A brahmana does not know that Lord always protects His devotee. The devotee must risk everything in his possession for the service of the Lord, but he is always protected and never defeated.
By materialistic calculations, Shukracharya thought that Bali Maharaja would under no circumstances be able to keep his promise to the brahmachari, Lord Vamanadeva.
Bali Maharaja considered that Shukracharya was no longer to be accepted as a spiritual master, for he had deviated from the duty of a spiritual master.
According to shastra, one should not become a guru if he cannot enable his disciple to advance in Krishna consciousness. The goal of life is to become a devotee of Lord Krishna so that one may be freed from the bondage of material existence. The spiritual master helps the disciple attain this stage by developing Krishna consciousness.
Also the duty of the guru is to take the disciple back home, back to Godhead. If he is unable to do so and instead hinders the disciple in going back to Godhead, he should not be a guru. Gurur na sa syät (SB 5.5.18).
Here Shukracharya has advised Bali Maharaja to deny the promise to Vamanadeva. Under these circumstances, therefore, Bali Maharaja thought that there would be no fault if he disobeyed the order of his spiritual master. He decided that Lord Vishnu should be pleased in all circumstances, even at the risk of ignoring the guru's advice to the contrary.
Anyone who is supposed to be a guru but who goes against the principle of Vishnu-bhakti cannot be accepted as guru. If one has falsely accepted such a guru, one should reject him.
Srila Jiva Gosvami has advised that such a useless guru, a family priest acting as guru, should be given up, and that the proper, bona-fide guru should be accepted.
"A scholarly brahmana expert in all subjects of Vedic knowledge is unfit to become a spiritual master without being a Vaishnava, but if a person born in a family of a lower caste is a Vaishnava, he can become a spiritual master." (Padma Purana)
A devotee is determined to serve the Supreme Personality of Godhead to His full satisfaction. Anything that hampers such determination should certainly be rejected. This is the principle of bhakti.
Anukulyasya sankalpaù pratikulyasya varjanam (Cc. Madhya 22.100). To perform devotional service, one must accept only that which is favorable and reject that which is unfavorable.
Bali Maharaja had the opportunity to contribute everything he possessed to the lotus feet of Lord Vamanadeva, but Shukracharya was putting forward a material argument to hamper this process of devotional service.
Under the circumstances, Bali Maharaja decided immediately to reject the advice of Shukracharya and go on with his duty. Thus he gave all his possessions to Lord Vamanadeva.
(Srimad Bhagavatam Canto 8, Chapter 20, Purport of Verse1)