When transcendental devotional service, by which love for Krishna is attained is executed by the senses, it is called Saadhana Bhakti, or the regulative discharge of devotional service. Such devotion eternally exists within the heart of every living entity. The awakening of this eternal devotion is the potentiality of devotional service in practice. — Sri Caitanya Caritamrta, Madhya Lila, 22.105.
Devotional Service is just like a seed sown in the heart of a living entity and if he goes on hearing & chanting, that seed fructifies, just as the seed of a tree fructifies with regular watering. Thus the spirtitual plant of devotional Service grows gradually.
Out of many millions of wandering living entities, one who is very fortunate gets an opportunity to associate with a bonafide spiritual master by the grace of Krishna. By the mercy of both Krishna and the spiritual masters, such a person receives the seed of the creeper of devotional service.
The human body is rarely achieved and although temporary like other bodies, it is meaningful because in human life one can perform devotional service. Even a slight amount of sincere devotional service can give one complete perfection.