Śrīla Bhakti Rakṣak Śrīdhar Dev-Goswāmī Mahārāj explains the definition of pure devotion.
hṛṣīkeṇa hṛṣīkeśa-sevanaṁ bhaktir uchyate
Devarṣi Nārad has given a definition of pure devotion (śuddha-bhakti). Sarvopādhi-vinirmuktaṁ: the ātma [self] is within, but there are so many covers (upādhis) over it: the annamaya-kośa, prāṇamaya-kośa, manamaya-kośa, and jñānamaya-kośa—the body, the vital energy, the mind, and the intelligence. Devotion must be independent of all of these covers. Devotion’s purity depends on the extent to which it is uncontaminated by the interest of these covers. Furthermore, Tat-paratvena nirmalam: how much is one’s devotion dedicated towards the centre? Tat means the centre, Kṛṣṇa, the Absolute. How much is one’s devotion in the interest of the Centre? The purity of one’s actions will be measured by this criterion. Hṛṣīkeṇa Hṛṣīkeśa-sevanaṁ: whatever you do outwardly—with the hands, eyes, ears, mind, or any other channel or acquired means—must be meant for the satisfaction of the Centre and not for any agency within the covers over the self.
This definition has been quoted when Śrīla Rūpa Goswāmī gives his definition of pure devotion:
ānukūlyena kṛṣṇānuśīlanaṁ bhaktir uttamā
Kṛṣṇānuśīlanam: culture Kṛṣṇa in any way; contact Him by any means and culture: speak about Him, hear about Him, and serve Him. What you do does not matter. But whatever you do must be anyābhilāṣitā-śūnyaṁ, free from the fleeting desires that come along at any and all times without rhyme or reason. Then jñāna-karmādy-anāvṛtam. Karma means systematic, moral, ‘God-touching’ activity. Jñān means knowledge that encourages us to be aloof, to be free from the material atmosphere’s mortal contact. Karma and jñān are both negative, undesireable engagements [they do not bring satisfaction to the Lord]. Kṛṣṇānuśilanam must independent of these interests. No representation of the covers over the soul should remain within it.
Another important thing is last: “Ānukūlyena Kṛṣṇānuśīlanaṁ: try to withdraw from the camp of those who are opposed to the Lord’s pleasure. There is a party that is satisfying, trying to satisfy, Kṛṣṇa. To make Kṛṣṇa’s service more intense, an opposite is necessary, and there is competition against them. Try to avoid that opposition camp and follow the direct service camp.
Elimination is necessary there also [in the spiritual world]. First you are to eliminate anyābhilāṣ, karma, and jñān. Then, when you enter Vaikuṇṭha, you are to eliminate the opposition party. You will have to be careful that you will not be taken by the opposition party. Try to stay on the side of the direct service party, the direct current. This warning is also given by Rūpa Goswāmī: ānukūlyena, not prātikūlyena [be favourable, not unfavourable, to the Lord’s desires].
Śiṣupāl, Kaṁsa, and others are a part of Kṛṣṇa’s Pastimes, but such a part is not desireable for us. We shall try to enter into the positive service party, not the indirect camp. This is śuddha-bhakti. Rūpa Goswāmī has given us this warning.
In Bhāgavatam, it is generally mentioned:
sambandhād vṛṣṇayaḥ snehād yūyaṁ bhaktyā vayaṁ vibho
“We can get out of this mundane world by accepting any connection with Kṛṣṇa.”
It is true. Fear, jealousy, or lust to enjoy Kṛṣṇa and His form can get you relief from this mundane world. But in the upper stage, there is consideration of good or bad in this regard.
tad brahma-kṛṣṇayor aikyāt kiraṇārkopamā-juṣoḥ
It is said in the scriptures many times that the demons killed by Kṛṣṇa get liberation. But that liberation and the liberation attained by a devotee are not one and same. Those whom Kṛṣṇa kills go to Brahmaloka; they do not reach Kṛṣṇa Himself. Kiraṇārkopamā-juṣoḥ: the difference between these attainments is like the difference between the sun and its rays. Fear, enmity, lust, and so on, in connection of Kṛṣṇa, lead one to Brahmaloka. Also, to be killed by Kṛṣṇa has some advantage and leads one up to Brahmaloka, but no further. Only Kṛṣṇa’s service takes us higher; only by service can we go higher than Brahmaloka.
Yad-arīṇāṁ means enemies, and priyāṇāṁ means devotees. Prāpyam ekam ivoditam: their attainment is almost one and the same. This is said in many places in śāstra: “Come into any connection with Kṛṣṇa, and you will get salvation.” But prāpyam ekam ivoditam is a rough statement. It refers only to a general similarity. Tad Brahma-Kṛṣṇayor aikyāt kiraṇārkopamā-juṣoḥ: if you scrutinise the gain of the Lord’s enemies and devotees, then you will find that there is a great difference. One group goes to Brahmaloka, which is compared to a ray of the sun, and the other group enters the domain of the sun. In this way we are to adjust.
So ānukūlyena Kṛṣṇānuśīlanaṁ bhaktir uttamā gives us a warning: try to side with the positive line of service, and not go to the other camp, the camp of those who are posted in the opposition party. Your inner temperament will be such. Sevonmukhatā [the intention to serve] and ānukūlya [adjusting to what is pleasing to the Lord] should be our guides always. We shall always keep this in mind: the straight way. Not this party, that party, or any subsidiary parties, but the main party, the main road. We shall go straight; we shall always try to go straight.
Nitāi Gauraharibol Nitāi Gauraharibol.
“As many souls attain liberation by absorbing their minds in the Lord with devotion, so many other souls attain liberation by absorbing their minds in the Lord out of lust, enmity, fear, or affection.”
sambandhād vṛṣṇayaḥ snehād yūyaṁ bhaktyā vayaṁ vibho
“The gopīs by their lust, Kaṁsa by his fear, Śiśupāl and other kings by their enmity, the Vṛṣṇis by their familial relationship, the Pāṇḍavas by their affection, and the ṛṣis by vaidhī-bhakti, attained liberation (though more specifically, the gopīs attained prema, Kaṁsa attained sāyujya-mukti, Śiśupāl attained sāyujya-mukti and later sarūpya-mukti, and the Vṛṣṇis, Pāṇḍavas, and ṛṣis attained salokya-mukti).