Actually, bhakti should be automatic and spontaneous. There should be no motive in serving Krishna, but even if there is a motive, service rendered unto Krishna is good. Even if one approaches Krishna with some ulterior motive, one is considered pious. For instance, Dhruva Maharaja initially worshiped Krishna with a motive, but after attaining perfection in devotional service, his ulterior motive vanished. When he actually saw Krishna, he said, “I do not want anything from You. I don’t want any benediction other than Your service.” After hearing about the many transcendental qualities of Krishna, if we somehow or other become attracted to Krishna consciousness, our lives will be successful. Tasmat kenapy upayena manah krsne nivesayet: “Somehow or other we have to attach our minds to Krishna consciousness.” (BG 7.1.32) Then Krishna will help us and give us intelligence from within.
Source: A.C. Bhaktivedanta Swami Prabhupada (2007 edition), “Teachings of Lord Kapila, The Son of Devahuti”, Page 181