It is the opinion of expert devotees that mental speculation and the artificial austerities of yoga practice may be favorable for becoming liberated from material contamination, but they will also make one's heart harder and harder. They will not help at all in the progress of devotional service. These processes are, therefore, not favorable for entering into the transcendental loving service of the Lord. Actually Kṛṣṇa consciousness—devotional service itself—is the only way of advancing in devotional life. Devotional service is absolute; it is both the cause and the effect. The Supreme Personality of Godhead is the cause and effect of all that be, and to approach Him, the absolute, the process of devotional service—which is also absolute—has to be adopted.
This is confirmed in the Bhagavad-gītā by the Lord Himself: "One can understand Me only through devotional service." In beginning His teaching of the Gītā, the Lord said to Arjuna, "Because you are My devotee I shall teach these secrets to you." Vedic knowledge means ultimately to understand the Supreme Lord, and the process of entering into His kingdom is devotional service. That is accepted by all authentic scriptures. Mental speculators neglect the process of devotional service, and by simply trying to defeat others in philosophical research they fail to develop the ecstasy of devotion.
In the Eleventh Canto, 20th Chapter, 31st verse, of the Śrīmad-Bhāgavatam, Kṛṣṇa says, "My dear Uddhava, for persons who are seriously engaged in My service, the cultivation of philosophical speculation and artificial renunciation are not very favorable. When a person becomes My devotee he automatically attains the fruits of the renunciation of material enjoyment, and he gets sufficient knowledge to understand the absolute truth." That is the test of advancement in devotional service. A devotee cannot be in darkness because the Lord shows him special favor and enlightens him from within.
In the Eleventh Canto, 20th Chapter, 32nd and 33rd verses, of the Śrīmad-Bhāgavatam the Lord further instructs Uddhava: "My dear friend, the profits derived from fruitive activities, austerities, the culture of philosophical knowledge, renouncement, the practice of mystic yoga, charity and all similar auspicious activities are automatically achieved by My devotees—those who are simply attached to Me by loving service. These devotees have everything at their disposal, but they desire nothing outside of My devotional service. If ever a devotee should desire some material profit—to be promoted to the heavenly planets—or some spiritual profit—to go to the Vaikuṇṭhas—by My causeless mercy their desires are very easily fulfilled."
Actually a person who is developing Kṛṣṇa consciousness and still has some attachment to material enjoyment will soon be freed from such a tendency by regularly discharging devotional service under the instruction of a bona fide spiritual master.
Śrīla Rūpa Gosvāmī, then, recommends that one should not be attached to material sense enjoyment, but accept everything enjoyable which is in relationship to Kṛṣṇa. For example, eating is necessary, and one wants some palatable dishes to satisfy his sense of taste. So in that case, for the satisfaction of Kṛṣṇa rather than for the satisfaction of the tongue, some palatable dishes may be prepared and offered to Kṛṣṇa. Then it is renunciation. Let the palatable dishes be prepared, but unless they are offered to Kṛṣṇa one should not accept them for eating. This vow of rejecting anything which is not offered to Kṛṣṇa is actually renunciation. And by such renunciation one is able to satisfy the demands of the senses.