CC Madhya 19.213
This verse is from Śrīmad-Bhāgavatam (11.19.36). The conditioned soul under the clutches of māyā, the material energy, is very much agitated by the urges of the tongue and the genitals. Control of the urges of the tongue, the belly and the genitals (which are situated in a straight line) is called dhṛti. Śrīla Bhaktivinoda Ṭhākura says, tāra madhye jihvā ati, lobhamaya sudurmati. Among the senses, the tongue is the most formidable enemy of the conditioned soul. Urged by the tongue, one commits many sinful activities. Although Kṛṣṇa has given human beings nice food, people still commit sins by killing poor animals for the satisfaction of the tongue. Not being able to control the tongue, the conditioned soul eats more than he needs. Of course, everyone must eat to keep the body fit for the Lord’s service, but when one cannot control the senses, he falls victim to the dictations of the tongue and the belly. Naturally, genital agitation follows, and one seeks illicit sex. However, if one is fixed at the lotus feet of Kṛṣṇa, he can control the tongue. Bhaktivinoda Ṭhākura further states, kṛṣṇa baḍa dayāmaya, karibāre jihvā jaya, sva-prasāda-anna dilā bhāi: in order to conquer the tongue, Kṛṣṇa has been very merciful and has given us nice food that has been offered to Him. When a person is attached to Kṛṣṇa’s lotus feet, he does not eat anything not offered to Kṛṣṇa. Sei annāmṛta khāo, rādhā-kṛṣṇa-guṇa gāo, preme ḍāka caitanya-nitāi. Since a devotee eats only prasādam, he conquers the dictations of the tongue, belly and genitals. One can control the dictates of the senses when situated in the position of śānta-rasa. Then one’s advancement in Kṛṣṇa consciousness is assured.