Rupa Gosvami says that spiritual life can be advanced, the first principle is utsaha. Utsahat. Utsaha means enthusiasm: "Yes, Krsna says, sarva-dharman parityajya mam ekam saranam vraja [Bg. 18.66]. I will accept it and work enthusiastically on the principle, as Krsna says." Krsna says, man-mana bhava mad-bhakto mad-yaji mam namaskuru [Bg. 18.65], and we have to do it,
execute it enthusiastically: "Yes, I shall always think of Krsna." Man-manah. Krsna says directly, man-mana bhava mad-bhaktah, "You just become My devotee." So we have to be enthusiastic, "Yes, I shall become Krsna's devotee." Man-mana bhava mad-bhakto mad-yaji. Krsna says, "Worship Me," so we should be very much enthusiastic to worship Krsna, offer mangala-arati,
rise early in the morning. These are all enthusiasm, utsaha. Those who are not enthusiastic — lazy, lethargetic — they cannot advance in spiritual life. Simply sleeping, they cannot make. One must be very, very enthusiastic, positive.

Srila Prabhupada, Srimad-Bhagavatam 3.26.30 — January 7, 1975, Bombay