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's) 
The Personality of Godhead, Lord Krsl1a [Govindal, 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)