Within the path of Bhakti Yoga, the shastras outline nine primary processes of devotional service, starting with śravaṇaṁ (hearing), kīrtanaṁ (chanting), and smaraṇaṁ (remembering the Lord). Among these, kīrtanaṁ—specifically the chanting of the Lord's holy names—is declared by the previous acharyas (spiritual masters) to be the most important and the root of all other devotional activities.
Srila Jiva Goswami explains that while there are other powerful processes of bhakti, such as deity worship or rendering physical service, their effectiveness in the current age is heavily dependent on being accompanied by the chanting of the holy name. Chanting nourishes all other limbs of devotional service. When we chant, we are simultaneously hearing (śravaṇaṁ), vibrating the name (kīrtanaṁ), and naturally remembering the Lord (smaraṇaṁ).
Sri Caitanya Mahaprabhu focused His entire movement on nama-sankirtana (the congregational chanting of the holy names) because it acts as the lifeblood of a devotee. Just as watering the root of a tree automatically nourishes the branches, leaves, and flowers, pouring one’s energy into sincerely chanting the Hare Krishna mahāmantra automatically awakens all good qualities and brings success in every other aspect of one's spiritual life.