Religion without philosophy is sentiment, or sometimes fanaticism, while philosophy without religion is mental speculation.

His Divine Grace A.C. Bhaktivedanta Prabhupada
Bhagavad-gita As It Is 3.3, Purport

All kinds of activities, both auspicious and inauspicious, that are detrimental to the discharge of transcendental loving service to Lord Sri Krsna are actions of the darkness of ignorance.

Krsnadasa Kaviraja Gosvami
Sri Caitanya-caritamrta, Adi-lila 1.94

Even though one may be very learned and wise, he is mad if he does not understand that the endeavor for sense gratification is a useless waste of time. Being forgetful of his own interest, he tries to be happy in the material world, centering his interests on his home, which is based on sexual intercourse and which brings him all kinds of material miseries. In this way one is no better than a foolish animal.

Lord Rsabhadeva
Srimad-Bhagavatam 5.5.7

In this material world the living entity's only business is to accept the path of bhakti-yoga and chant the holy name of the Lord.

Sri Yamaraja
Srimad-Bhagavatam 6.3.22

Sri Krsna, the Personality of Godhead, who is the Paramatma [Supersoul] in everyone's heart and the benefactor of the truthful devotee, cleanses desire for material enjoyment from the heart of the devotee who has developed the urge to hear His messages, which are in themselves virtuous when properly heard and chanted.

Suta Gosvami
Srimad-Bhagavatam 1.2.17

Whatever a devotee experiences he should consider to be an expansion of Krsna. Thus seeing everything that exits within creation as the body of the Supreme Lord, Hari, the devotee should offer his sincere respects to the entire expansion of the Lord's body.

Kavi Rsi
Srimad-Bhagavatam 11.2.41

Only unto those great souls who have implicit faith in both the Lord and the spiritual master are all the imports of Vedic knowledge automatically revealed.

Svetasvatara Upanisad 6.23