Śrīla Bhakti Siddhānta Saraswatī Ṭhākur explains the plight of those who insincerely practice devotion.
The following is translation of the parable Dui Naukāya Pā, Feet in Two Boats, from a Bengali book of parables by Śrīla Bhakti Siddhānta Saraswatī Ṭhākur entitled Upākhyāne Upadeś.
Feet in Two Boats
If you put your feet into two boats, you will fall into deep water. If someone stands with their feet in two different boats while the boats are moving together, they can fall into the water if a gap opens between the boats. If the boats move in two different directions, you will not go in either of them. Rather, you will lastly fall into great danger.
Many say, “Make a family and pray to the Lord. Work with your hands and chant the Lord’s Name with your mouth.” This conception is comparable to putting your feet in two different boats. “I will make a family, and I will pray to the Lord”—this is impossible. One can remain in a family and serve the Lord. But that must be Kṛṣṇa’s family, not Māyā’s family. If one stays in Māyā’s family, one does not serve the Lord, and if one stays in Kṛṣṇa’s family, one does not serve Māyā. In Kṛṣṇa’s family, all activities are for the glorification of Kṛṣṇa’s Names and qualities—for the satisfaction of Kṛṣṇa’s senses, not for the sake of one’s own enjoyment or renunciation. If one only externally dresses as a sannyāsī, householder, or renunciant, one does not serve the Lord. When one does what pleases the Lord, that is, when one performs all of one’s actions with all of one’s senses in all circumstances under the guidance of Śrī Guru and the Vaiṣṇavas for the sake of benefitting other souls, tasting the Name, and serving the Vaiṣṇavas, then one fulfils one’s duty to Kṛṣṇa’s family and serves the Lord. The endeavour of one who tries to perform some actions for Kṛṣṇa’s enjoyment and some for one’s own enjoyment is no different than putting one’s feet in two boats.
Pure devotees always perform all of their actions for the sake of the Lord’s service. They do not even pass urine and stool for their own enjoyment. They do so only because it is conducive to serving the Lord. The fundamental purpose of all of their actions—eating, sleeping, walking, earning money, and so on—is the Lord’s service. But if someone insincerely says or thinks, “I am doing all of these things to serve the Lord” in order to continue their own enjoyment, then they do not serve the Lord. Genuine Gurus and Vaiṣṇavas spot all such insincerity. If one puts dust in others’ eyes (misleads them), indulges one’s own mind, and in this way puts one’s feet in two boats, one will eventually fall into distress, that is, one will fall in the river of Māyā and loose one’s life. Therefore, endeavouring to cross over the turbulent ocean of material existence by boarding only the boat captained by Śrī Guru and the sādhus is the sole engagement of the intelligent.
dui nāye nadī-pārera durdaśā labhibe
Jagāi says, “If you do not become singleminded, the plight of crossing a river in two boats will befall you.”