One’s only concern should be to satisfy the Lord by one’s activities. If the Lord is satisfied by an action, whatever it may be, then it is successful. Otherwise, it is simply a waste of time. That is the standard of all sacrifice, penance, austerity, mystic trance and other good and pious work.
His Divine Grace A. C. Bhaktivedanta Swami Prabhupada
Srimad-Bhagavatam 3.9.41, Purport

Do not be preoccupied with the end result of chanting. Rather, chant Krishna’s name constantly with patience and forbearance. The Lord will surely not sit silently and do nothing. . . . As you run your hands over the japa mala, think that you are touching Lord Gaurasundara’s [Chaitanya’s] lotus feet. That is the way you should chant.
Srila Bhaktisiddhanta Sarasvati Thakura
Srila Prabhupadera Patravali, Vol. II, p. 10

O son of Kunti [Arjuna], one who becomes joyful upon seeing a person who is inclined to chant the holy names of the Lord will also go back to Godhead and enjoy the association of Lord Vishnu. Therefore, My advice is that you go on chanting My holy names with firm determination, because one who is attached to chanting My holy names is very dear to Me.
Lord Sri Krishna
Adi Purana, quoted in Hari-bhakti-vilasa 11.470–1

When one accepts the Vedic literature by interpretation or even by dictionary meaning, directly or indirectly the ultimate declaration of Vedic knowledge points to Lord Krishna.
Sri Chaitanya Mahaprabhu
Sri Chaitanya-charitamrita, Madhya 20.146

It is the duty of every conditioned soul to engage his polluted consciousness, which is now attached to material enjoyment, in very serious devotional service with detachment. Thus his mind and consciousness will be under full control.
Lord Kapila
Srimad-Bhagavatam 3.27.5

A person who is engaged in devotional service in full Krishna consciousness is to be understood to be doing the best service to the whole world and to be pleasing everyone in the world. In addition to human society, he is pleasing even the trees and animals, because they also become attracted by such activities.
Srila Rupa Goswami
Bhakti-rasamrita-sindhu 1.1.28

Go ahead and worship Lord Brahma! Go ahead and worship Lord Shiva! Go ahead and worship the Supreme Brahman! I will not follow you. I will simply worship Vrindavan forest, which brought transcendental delight to Lord Krishna.
Author unknown
Srila Rupa Goswami’s Padyavali 126

Only the wise person who can see that Supreme Soul within his heart becomes peaceful and enjoys transcendental bliss.
Katha Upanishad 2.2.12–13