In plain words
Be he one versed in the sum of all the śāstras and Purāṇas, a sage who knows what Vedānta teaches; be he one who, with delight overflowing, in lovely mansions takes his pleasure, a moon among kings; be he one who has routed his foes on the battlefield and shines, the one hero of the world; be he one who languishes at the mercy of the goddess of poverty, a servant who is the lord of ill fortune: if he has no Bhakti, he is of no use at all. Rather than that lord of the world who lacks Bhakti, the servant who is a devotee is the nobler.
Anirvacanīyam bhakti. It cannot be described. Among all the many sādhanas in the world, Bhakti is easy. It is the highest. The word bhakti is formed when the suffix ti is joined to the root bhaj. Bhakti means service. Attendance. It is friendship mingled with fear. In measuring the principle made of the three guṇas against the power beyond the three guṇas, humility and obedience too are, to some extent, essential. Bhaja sevāyām. To serve the Divine with the three guṇas, through the actions of mind, speech and body, is Bhakti. Bhakti means perfect Prema. Bhakti and Prema are bound in an inseparable relation. The two depend on each other. Bhakti is the sādhana for Mukti. The form of Bhakti is Prema. To serve God with unbroken Prema is the chief Bhakti: that is Nārada's view. That which holds Prema and fond attachment in worship and in offering: that is the view of Vyāsa. The citta that renders service with purity of thought, word and deed and makes an offering of itself: that, in the opinion of the ṛṣi Gārga, is Bhakti. To hold the mind in check, turn it towards God and experience divine Ānanda is true Bhakti: that is Yājñavalkya's view. Great souls have taught in many ways that Bhakti is to turn the citta towards the Ātma and experience the Ānanda of oneness; yet, all said and done, what is chief is Prema, that one thing only.