Hardness of the heart is compared to a lightning bolt, with gold and with shellac. The lightning bolt is very strong and never becomes soft. Similarly, the hearts of those who are engaged in severe austerities and penances do not become very easily softened. The golden heart becomes melted at high temperature, as in ecstatic love. And the shellac heart is very easily melted in slight temperature.
Softness of the heart is compared with honey, with butter and with nectar. And the condition of the mind is compared with sunshine. As honey and butter become melted even in slight sunshine, so softhearted persons become easily melted. Nectar, however, is by its nature always liquid. And the hearts of those who are in pure ecstatic love with Kṛṣṇa are by nature always liquified, just like nectar.
A pure devotee of Kṛṣṇa is always specifically qualified with nectarean qualifications and sometimes with the qualifications of butter and honey. On the whole, all the different conditions of the heart mentioned above can be melted under certain circumstances, just as a hard diamond sometimes is melted by a combination of certain chemicals. In the Dāna-keli-kaumudī it is stated, "When love develops in the heart of a devotee, he cannot check the transformation of his sentiments. It is just like at the rising of the moon, when the ebb tide of the ocean cannot be checked: immediately there must be movement of high waves." Although in its natural state, the ocean is always very grave and unfathomable, when the moon rises, nothing can check the ocean's agitation. Similarly, those who are pure devotees cannot on any account check the movements of their feelings within.