One has to learn to use a typewriter by following the regulative principles of the typing book. One has to place his fingers on the keys in such a way and practice, but when one becomes adept, he can type swiftly and correctly without even looking at the keys. Similarly, one has to follow the rules and regulations of devotional service as they are set down by the spiritual master; then one can come to the point of spontaneous loving service.
His Divine Grace A. C. Bhaktivedanta Swami Prabhupada
Sri Chaitanya-charitamrita, Madhya-lila 22.109, Purport

Out of pity for the apostate jivas, God sends His own messenger into this world in every age for establishing the pure and eternal religion in the form of constant service of Krishna. Either Krishna or Krishna’s own messenger establishes the true and eternal religion in this world. This task is beyond the capacity of those who are not helped by the grace of God himself.
Srila Bhaktisiddhanta Sarasvati Thakura
Amrita-vani, Section: “108 Essential Instructions”

The one Supreme Lord is situated within all material bodies and within everyone’s soul. Just as the moon is reflected in innumerable reservoirs of water, the Supreme Lord, although one, is present within everyone. Thus every material body is ultimately composed of the energy of the one Supreme Lord.
Lord Sri Krishna
Srimad-Bhagavatam 11.18.32

What grateful soul is there who would not render his loving service to such a great master as the Personality of Godhead? The Lord can be easily pleased by spotless devotees who resort exclusively to Him for protection, though the unrighteous man finds it difficult to propitiate Him.
Sri Suta Goswami
Srimad-Bhagavatam 3.19.36

The liberated souls enjoy the Supreme Lord’s company. They enjoy pastimes with the Lord.
Chandogya Upanishad 7.25.2

For one who has Govinda in his heart, Kali-yuga becomes Satya-yuga. And for one who does not have Acyuta in his heart, Satya-yuga becomes Kali-yuga.

Each name of Vishnu is greater than all the Vedas.
Padma Purana
“Glorification of the 108 Names of Rama”

Bhakti is bhajanam, or devotional service to Krishna. It is concentration of the mind on Krishna without desires for enjoyment in this life or the next. It destroys all karma.
Gopala-tapani Upanishad 1.14

Those who perform bhakti have no inauspiciousness in this life or the next. They lead millions of their family members to the spiritual world.
Lord Vishnu
Skanda Purana, Dwaraka-mahatmya