Śrīla Bhakti Siddhānta Saraswatī Ṭhākur explains the foremost duty of every soul.
Translated from the original Bengali quotation published in Śrī Gauḍīya Darśan, Volume 5, Issue 2, Sunday 13 September 1959.
We must take shelter of the Lord, who is replete with all virtues. If we do so, then we will no longer have to be goaded by the three modes and spend our life restless in thought of enjoying the modes or renouncing them. Let our entire thought process run towards the Whole. By doing so, no unwholesomeness will remain any longer. The soul has no duty other than service to the Supreme Soul, and apart from that, the soul has no unending joy.
avismṛtiḥ kṛṣṇa-padāravindayoḥ
kṣiṇoty abhadrāṇi cha śaṁ tanoti
sattvasya śuddhiṁ paramātma-bhaktiṁ
jñānañ cha vijñāna-virāga-yuktam
(Śrīmad Bhāgavatam: 12.12.55)
[“Non-forgetfulness of Kṛṣṇa’s lotus feet dispels all inauspiciousness and produces good fortune, purification of the heart, devotion to the Supreme Lord, and knowledge enriched with realisation and detachment.”]
When we can apply in all our formal activities the conception of service to the Lord present in this verse from the conclusion of Śrīmad Bhāgavatam, then apart from such joy (rasa), we will have no taste for any sort of mundane joy. Only when we become estranged from the complete proprietor of genuine and auspicious joy—of our own personal joy—do we encounter obstacles to complete joyfulness.
We do not see any proper course other than not coming under the sway of relative dharmas. Apart from seeing form with the eye or hearing sound with the ear, we do not see that the eyes and ears have any other function. When we engage our eyes, ears, and so forth in the study of objects that can be measured rather than the object of our eternal, spiritual joy, that is, when we become bound in the steam of illusory thought, then we part with the conceptions of “non-forgetfulness of Kṛṣṇa’s lotus feet” and “always chant the Name of the Lord” and become troubled by various vices (anarthas).
Kīrtanīyaḥ sadā Hariḥ [“Always chant the Name of the Lord”]—this is the teaching of Lord Śrī Chaitanyadev. All our problems arise only from a scarcity of such glorification of the Lord (Hari-kīrtan). Although the temporary necessity of worldly activities is certainly accepted by those who are fit for them, considering the future results produced by such activities is the duty of every intelligent person. Thus, Mahāprabhu said, “Kīrtaṇīyaḥ sadā Hariḥ: always chant the Name of the Lord.”