The most confidential part of knowledge is that one should become a pure devotee of Krsna and always think of Him and act for Him. . . . He should arrange his life in such a way that throughout the twenty-four hours he cannot but think of Krsna. And the Lord's promise is that anyone who is in such pure Krsna consciousness will certainly return to the abode of Krsna, where he will engage in the association of Krsna face to face.

His Divine Grace A. C. Bhaktivedanta Swami Prabhupada
Bhagavad-gita As It Is, 18.65, Purport

The residents of both heaven and hell desire human birth on the earth planet because human life facilitates the achievement of transcendental knowledge and love of Godhead, whereas neither heavenly nor hellish bodies efficiently provide such opportunities.

Lord Sri Krsna
Srimad-Bhagavatam 11.20.12

Those who are fortunate to receive the teachings of Lord Caitanya can progress very quickly. In a short life span, a person can easily progress from varnasrama to the highest level of prema, pure love of God.

Srila Bhaktivinoda Thakura
Sri Caitanya Siksamrta, Chapter 3, Part 1

One has to have great strength of mind to know the truth. If one wants to learn to swim, he must not be afraid of water. At the same time, one should know that saranagati, or the path of exclusive surrender, is not a difficult thing. In fact, it is very easy and natural for the soul. Anything which is opposed to it—that is unnatural and painful.

Srila Bhaktisiddhanta Sarasvati Thakura
Reply to a disciple's question

The Personality of Godhead, Lord Krsna [Govinda], is the exclusive shelter for all great living beings, and His transcendental attributes cannot even be measured by such masters of mystic powers as Lord Siva and Lord Brahma. Can anyone who is expert in relishing nectar [rasa] ever be fully satiated by hearing topics about Him?

Sages of Naimsaranya
Srimad-Bhagavatam 1.18.14

Material enjoyments are full of poison, but you consider them pleasing. Do not think of them as a source of happiness, but understand them as distress. Be absorbed in full thought of Govinda, associate with His devotees, and conclude that devotional service is the goal of life.

Srila Narottama Dasa Thakura
Sri Prema Bhakti Candrika