Cleanliness is essential for making advancement in spiritual life. There are two kinds of cleanliness: external and internal. External cleanliness means taking a bath, but for internal cleanliness one has to think of Krishna always and chant Hare Krishna, Hare Krishna, Krishna Krishna, Hare Hare/ Hare Rama, Hare Rama, Rama Rama, Hare Hare. This process cleans the accumulated dust of past karma from the mind.
Bhagavad Gita 13.8-12,
Any person who is chanting the holy names of Krishna (Hare Krishna, Hare Krishna, Krishna Krishna, Hare Hare/ Hare Rama, Hare Rama, Rama Rama, Hare Hare) in course of chanting without offenses feels some transcendental pleasure and very quickly becomes puriﬁed of all material contamination.
Bhagavat Gita 9.2,
Happiness derived from a combination of the senses and the sense objects is always a cause of distress and should be avoided by all means.
Bhagavad Gita 18.38,
The best means of spiritual realization is chanting the holy name of the Lord.
Bhagavad Gita 6.11-12,
Bhagavad Gita is also known as Gitopaniṣad. It is the essence of Vedic knowledge and one of the most important Upanisads in Vedic literature.
Bhagavad Gita Introduction,
Bhagavad-gita is the instruction given by Krishna, and Srimad-Bhagavatam is the book containing topics exclusively about Krishna and His devotees. These two books are the special nectar of the words of Krishna.
Srimad Bhagavatam 4.4.44,