In this Age of Kali there are no genuine religious principles other than those established by Vaiṣṇava devotees and Vaiṣṇava scriptures. This is the sum and substance of everything.

In this age a person should not envy Śrī Caitanya Mahāprabhu's movement but should chant the holy names of Hari and Kṛṣṇa, the mahā-mantra. That is the sum and substance of the eternal religion, known as sanātana-dharma. Cc. Madhya 9.362

In Kali-yuga Krsna incarnated as th holy name inorder to deliver the sinful, who are suffering greatly.

As the Lord says in Bhagavad-gītā (4.7):

  “Whenever and wherever there is a decline in religious practice, O descendant of Bharata, and a predominant rise of irreligion—at that time I descend Myself.” In the present age, Kali-yuga, people are very much sinful and are consequently suffering greatly. Therefore Kṛṣṇa has incarnated in the form of His name, as found in the mahā-mantra: Hare Kṛṣṇa, Hare Kṛṣṇa, Kṛṣṇa Kṛṣṇa, Hare Hare/ Hare Rāma, Hare Rāma, Rāma Rāma, Hare Hare.
TQK (p. 203)

Because Kali-yuga is such a degraded and miserable age, Lord Caitanya advises everyone simply to chant Hare Krsna.

According to the Vedic conception, there must be men in society who are factually brāhmaṇas, capable of expounding the real truth. If everyone becomes a śūdra, the Absolute Truth cannot be understood. It is said that at the present moment in Kali-yuga everyone is a śūdra (kalau śūdra-sambhavāḥ), and it is very difficult in this age to find qualified brāhmaṇas, for they are very rare. There is practically not a single qualified brāhmaṇa in this age.

  “O learned one, in this iron age of Kali men have but short lives. They are quarrelsome, lazy, misguided, unlucky and, above all, always disturbed.” (Bhāg. 1.1.10) The people in this age are very short-lived and slow in understanding spiritual life. Actually human life is meant for understanding spiritual values, but because everyone in this age is a śūdra, no one is interested. People have forgotten life’s real purpose. The word manda means both slow and bad, and everyone in this age is either bad or slow or a combination of both. People are unfortunate and disturbed by so many things. According to Śrīmad-Bhāgavatam there will eventually be no rain and consequently a scarcity of food. The governments will also levy very heavy taxes. The characteristics of this age predicted by Śrīmad-Bhāgavatam are already being experienced to some degree. Since Kali-yuga is a very miserable age, Caitanya Mahāprabhu, who is Śrī Kṛṣṇa Himself, advises everyone simply to chant Hare Kṛṣṇa.

  “In this age of Kali there is no alternative, there is no alternative, there is no alternative for spiritual progress than the holy name, the holy name, the holy name of the Lord.” (Bṛhan-nāradīya Purāṇa) This process is not Caitanya Mahāprabhu’s invention, but is advised by the śāstras, the purāṇas. The process for this Kali-yuga is very simple. One need only chant the Hare Kṛṣṇa mahā-mantra.
TLK (pp.3-4)