In Kali-yuga the following is recommended:

harer nāma harer nāma
 harer nāmaiva kevalam
kalau nāsty eva nāsty eva
 nāsty eva gatir anyathā

(Bṛhan-nāradīya Purāṇa)

In order to be recognized by Kṛṣṇa, the Supreme Personality of Godhead, one should chant the holy name of the Lord continuously, twenty-four hours a day. Unfortunate persons who cannot accept this formula prefer to execute some type of pseudomeditation, without accepting the other processes of austerity. The fact is, however, that one must accept either the severe method of austerity described above to become purified or take to the process of devotional service recommended for pleasing the Supreme Lord, Kṛṣṇa. The person who is Kṛṣṇa conscious is most intelligent because in Kali-yuga it is not at all possible to undergo such severe austerities. We need only follow great personalities like Lord Caitanya Mahāprabhu. In His Śikṣāṣṭaka, Lord Caitanya Mahāprabhu wrote, paraṁ vijayate śrī-kṛṣṇa-saṅkīrtanam: all glories to the holy names of Lord Kṛṣṇa, which from the very beginning purify the heart and immediately liberate one. Bhava-mahādāvāgni-nirvāpanam. If the real purpose of all yoga is to please Lord Kṛṣṇa, then this simple bhakti-yoga system recommended for this age is sufficient. It is necessary, however, to engage constantly in the service of the Lord. Although Pṛthu Mahārāja executed his austerities long before the appearance of Lord Kṛṣṇa on this planet, his purpose was still to please Kṛṣṇa.

There are many fools who claim that worship of Kṛṣṇa began only about five thousand years ago, after the appearance of Lord Kṛṣṇa in India, but this is not a fact. Pṛthu Mahārāja worshiped Kṛṣṇa millions of years ago, for Pṛthu happened to be a descendant of the family of Mahārāja Dhruva, who reigned for thirty-six thousand years during the Satya-yuga age. Unless his total life span was one hundred thousand years, how could Dhruva Mahārāja reign over the world for thirty-six thousand years? The point is that Kṛṣṇa worship existed at the beginning of creation and has continued to exist throughout Satya-yuga, Tretā-yuga and Dvāpara-yuga, and now it is continuing in Kali-yuga. As stated in Bhagavad-gītā, Kṛṣṇa appears not only in this millennium of Brahmā’s life, but in every millennium. Therefore worship of Kṛṣṇa is conducted in all millenniums. It is not that Kṛṣṇa worship began only when Kṛṣṇa appeared on this planet five thousand years ago. This is a foolish conclusion that is not substantiated by Vedic literatures.

Also of significance in this verse are the words ārirādhayiṣuḥ kṛṣṇam acarat tapa uttamam: Mahārāja Pṛthu underwent severe types of austerities for the express purpose of worshiping Kṛṣṇa. Kṛṣṇa is so kind, especially in this age, that He appears in the transcendental vibration of His holy name. As is said in the Nārada-pañcarātra, ārādhito yadi haris tapasā tataḥ kim: if Kṛṣṇa is worshiped, if He is the goal of advancement, there is no need for one to execute severe types of tapasya, because one has already reached his destination. If, after executing all types of tapasya, one cannot reach Kṛṣṇa, all his tapasya has no value, for without Kṛṣṇa all austerity is simply wasted labor, śrama eva hi kevalam (Bhāg. 1.2.8). We should therefore not be discouraged just because we cannot go to the forest and practice severe austerities. Our life is so short that we must strictly adhere to the principles laid down by the Vaiṣṇava ācāryas and peacefully execute Kṛṣṇa consciousness. There is no need to become despondent. Narottama dāsa Ṭhākura recommends, ānande bala hari, bhaja vṛndāvana, śri-guru-vaiṣṇava-pade majāiyā mana: for a transcendental, blissful life, chant the Hare Kṛṣṇa mantra, come worship the holy place of Vṛndāvana, and always engage in the service of the Lord, of the spiritual master and of the Vaiṣṇavas. This Kṛṣṇa consciousness movement is therefore very safe and easy. We have only to execute the order of the Lord and fully surrender unto Him. We have only to execute the order of the spiritual master, preach Kṛṣṇa consciousness and follow in the path of the Vaiṣṇavas. The spiritual master represents both Lord Kṛṣṇa and the Vaiṣṇavas; therefore by following the instructions of the spiritual master and by chanting Hare Kṛṣṇa, everything will be all right.