Various demoniac states all over the world are increasing their military power in many ways, and the whole situation has become distressful. Therefore Krishna has appeared by His name, in the Hare Krishna movement, which will certainly diminish the burden of the world. Philosophers, religionists, and people in general must take to this movement very seriously, for man-made plans and devices will not help bring peace on earth.
His Divine Grace A. C. Bhaktivedanta Swami Prabhupada
Srimad-Bhagavatam 10.1.22, Purport

If one is infected with the desire for material enjoyment or material liberation, he cannot rise to the platform of pure loving service unto the Lord, even though he may superficially render devotional service according to the routine regulative principles.
Sri Chaitanya Mahaprabhu
Sri Chaitanya-charitamrita, Madhya-lila 19.175

If one has enthusiasm in the beginning of devotional service, and that enthusiasm does not become cold, then one will never become apathetic, lazy, or distracted in chanting the holy names. Therefore enthusiasm is the only support for all types of devotional service.
Srila Bhaktivinoda Thakura
Sri Bhaktyaloka, Chapter 7

O my Lord [Krishna]! Transcendental poets and experts in spiritual science could not fully express their indebtedness to You, even if they were endowed with the prolonged lifetime of Brahma, for You appear in two features – externally as the acharya and internally as the Supersoul – to deliver the embodied living being by directing him how to come to You.
Sri Uddhava
Srimad-Bhagavatam 11.29.6

Always remembering Me, one should perform all his duties for Me without becoming impetuous. With mind and intelligence offered to Me, one should fix his mind in attraction to My devotional service.
Lord Sri Krishna
Srimad-Bhagavatam 11.29.9

The . . . jiva is eternal and is for eternity and without a beginning joined to the Supreme Lord by the tie of an eternal kinship. He is transcendental spiritual potency.
Lord Brahma
Sri Brahma-samhita 5.21

The Vrajavasis’ affection for Sri Krishna is natural. One who is inspired by their loving moods must practice saadhana continuously in order to attain an emotional attachment just like theirs. Only then can this extremely rare loving attachment that is found in Vraja be attained.
Srila Jiva Goswami
Commentary on Sri Brahma-samhita 5.5

The Lord’s personal form possesses complete and faultless transcendental qualities. Indeed, the form of the completely independent Lord is free from all lifeless bodily characteristics. His lotus face and lotus feet consist simply of pure ecstasy.
Dhyana-bindu Upanishad