According to Sanskrit verbal arrangement, kurvanti refers to doing things for someone else. Therefore, it means that the ātmārāmas render devotional service unto the Lord not for personal interest but for the pleasure of the Lord, Urukrama.
Hetu means "causal." There are many causes for one's sense satisfaction, and they can be chiefly classified as material enjoyment, mystic powers and liberation, which are generally desired by progressive persons. As far as material enjoyments are concerned, they are innumerable, and the materialists are eager to increase them more and more because they are under the illusory energy. There is no end to the list of material enjoyments, nor can anyone in the material universe have all of them. As far as the mystic powers are concerned, they are eight in all (such as to become the minutest in form, to become weightless, to have anything one desires, to lord it over the material nature, to control other living beings, to throw earthly globes in outer space, etc.). These mystic powers are mentioned in the Bhāgavatam. The forms of liberation are five in number.
Therefore, unalloyed devotion means service to the Lord without desire for the above-mentioned personal benefits. And the powerful Personality of Godhead Śrī Kṛṣṇa can be fully satisfied by such unalloyed devotees free from all sorts of desires for personal benefit.
Unalloyed devotional service of the Lord progresses in different stages. Practice of devotional service in the material field is of eighty-one different qualities, and above such activities is the transcendental practice of devotional service, which is one and is called sādhana-bhakti. When unalloyed practice of sādhana-bhakti is matured into transcendental love for the Lord, the transcendental loving service of the Lord begins gradually developing into nine progressive stages of loving service under the headings of attachment, love, affection, feelings, affinity, adherence, following, ecstasy, and intense feelings of separation.
The attachment of an inactive devotee develops up to the stage of transcendental love of God. Attachment of an active servitor develops up to the stage of adherence, and that for a friendly devotee develops up to the stage of following, and the same is also the case for the paternal devotees. Devotees in conjugal love develop ecstasy up to the stage of intense feelings of separation. These are some of the features of unalloyed devotional service of the Lord.