One who is not envious but is a kind friend to all living entities, who does not think himself a proprietor and is free from false ego, who is equal in both happiness and distress, who is tolerant, always satisfied, self-controlled, and engaged in devotional service with determination, his mind and intelligence fixed on Me—such a devotee of Mine is very dear to Me. Coming again to the point of pure devotional service, the Lord is describing the transcendental qualifications of a pure devotee in these two verses. A pure devotee is never disturbed in any circumstances. Nor is he envious of anyone. Nor does a devotee become his enemy's enemy; he thinks, "This person is acting as my enemy due to my own past misdeeds. So it is better to suffer than to protest."
(Bhagavad-Gita-------12:13-14-------translation and purport).

The special qualification of the pure devotee is that he is always thinking of Kṛṣṇa without deviation and without considering the time or place. There should be no impediments. He should be able to carry out his service anywhere and at any time. Some say that the devotee should remain in holy places like Vṛndāvana or some holy town where the Lord lived, but a pure devotee can live anywhere and create the atmosphere of Vṛndāvana by his devotional service. It was Śrī Advaita who told Lord Caitanya, "Wherever You are, O Lord-there is Vṛndāvana."As indicated by the words satatam and nityaśaḥ, which mean "always," "regularly," or "every day," a pure devotee constantly remembers Kṛṣṇa and meditates upon Him. These are qualifications of the pure devotee for whom the Lord is most easily attainable. Bhakti-yoga is the system that the Gītā recommends above all others.
(Bhagavad-Gita-------8:14-------purport).

The particular word kṛṣṇa-devatāḥ, i.e., those who are always rapt in the service of Lord Kṛṣṇa, is significant. The Yādavas and the Pāṇḍavas, who were always rapt in the thought of the Lord Kṛṣṇa and His different transcendental activities, were all pure devotees of the Lord like Vidura. Vidura left home in order to devote himself completely to the service of the Lord, but the Pāṇḍavas and the Yādavas were always rapt in the thought of Lord Kṛṣṇa. Thus there is no difference in their pure devotional qualities. Either remaining at home or leaving home, the real qualification of a pure devotee is to become rapt in the thought of Kṛṣṇa favorably, i.e., knowing well that Lord Kṛṣṇa is the Absolute Personality of Godhead.
(Srimad Bhagavatam------1:13:11-------purport).