Everyone is searching after peace of mind. This is obtainable only when one is completely freed from the desire for material sense gratification and is engaged in the devotional service of the Lord.

His Divine Grace A. C. Bhaktivedanta Swami Prabhupada
Srimad-Bhagavatam 5.7.11, Purport

O my tongue, you are fond of sweet things and are of discriminating taste; I tell you the highest truth, which is also the most beneficial. Please just recite these sweet syllables: "Govinda," "Damodara," and "Madhava."

Srila Bilvamangala Thakura
Govinda Damodara Stotram 40

Simply by chanting the holy name of Lord Krsna, one can be freed from all undesirable habits. This is the means of awakening all good fortune and initiating the flow of waves of love for Krsna.

Sri Caitanya Mahaprabhu
Sri Caitanya-caritamrta, Antya-lila 20.11

O son of Prtha, a transcendentalist engaged in auspicious activities does not meet with destruction either in this world or in the spiritual world; one who does good, My friend, is never overcome by evil.

Lord Sri Krsna
Bhagavad-gita 6.40

It is not possible for worldly persons to understand, unassisted, the nature of spiritual living, because it is categorically different from the life currently led by them. This difference between the two is not confined to this or that isolated aspect. It is to be found in every single detail of conduct. The change from worldly to spiritual life is not of the nature of reform, but is truly a complete revolution.

Srila Bhaktisiddhanta Sarasvati Thakura
The Manifestation of Mercy (essay)

For a person devoid of devotional service, birth in a great family or nation, knowledge of the revealed scripture, performance of austerities and penance, and chanting of Vedic mantras are all like ornaments on a dead body. Such ornaments simply serve the concocted pleasures of the general populace.

Hari-bhakti-sudhodaya 3.12

It is true that by practicing restraint of the senses by the yoga system one can get relief from the disturbances of desire and lust, but this is not sufficient to give satisfaction for the soul, for this [satisfaction] is derived from devotional service to the Personality of Godhead.

Sri Narada Muni
Srimad-Bhagavatam 1.6.35