Those who are intelligent in this age take to sankirtana yajna rather than karma−kandiya−yajnas: It is said, tretayam yajato makhaih: in Treta−yuga, if one performed yajnas, he would get the results of those yajnas. By performing visnu−yajna specifically, one could even achieve the lotus feet of the Supreme Personality of Godhead. Of course, yajna is intended to please the Supreme Personality of Godhead... Yajnas for enjoyment of the senses are called karma−kandiya−yajnas... Karma−kandiya yajnas are meant for sensuous persons, whereas yajna should actually be performed to please the Supreme Personality of Godhead. To please the Supreme Personality of Godhead in Kali−yuga, the sankirtana−yajna is recommended. Yajnaih sankirtana−prayair yajanti hi sumedhasah [SB 11.5.32]. Only those who are very intelligent take to sankirtana−yajna to fulfill all their desires, material and spiritual, whereas those who are lusty for sense enjoyment perform karma−kandiya−yajnas.
¯Srimad−Bhagavatam 9.14.43
Because there are no qualified brahmanas and priests in Kali−yuga to perform Vedic sacrifices and chant Vedic mantras, only the sacrifice of chanting the Hare Krsna mantra is recommended: On the day of extracting the soma juice, King Yudhisthira very respectfully received the special priest who had been engaged to detect any mistake in the formalities of sacrificial procedures. The idea is that the Vedic mantras must be enunciated perfectly and chanted with the proper accent; if the priests who are engaged in this business commit any mistake, the checker or referee priest immediately corrects the procedure, and thus the ritualistic performances are perfectly executed. Unless it is perfectly executed, a sacrifice cannot yield the desired result. In this age of Kali there is no such learned brahmana or priest available; therefore, all such sacrifices are forbidden. The only sacrifice recommended in the sastras is the chanting of the Hare Krsna mantra.
¯Krsna, the Supreme Personality of Godhead
To perform a sacrifice successfully, at least four expert priests are needed: one who can offer (hota), one who can chant (udgata), one who can kindle the sacrificial fire without the aid of separate fire (adhvaryu), and one who can supervise (brahma). Such sacrifices were conducted from the birth of Brahma, the first living creature, and were carried on till the reign of Maharaja Yudhisthira. But such expert brahmana priests are very rare in this age of corruption and quarrel, and therefore in the present age only the yajna of chanting the holy name of the Lord is recommended.
The scriptures enjoin:
harer nama harer nama
harer namaiva kevalam
kalau nasty eva nasty eva
nasty eva gatir anyatha
[Adi 17.21]
The whole process of offering sacrifice is under the category of fruitive action, and such activities are extremely scientific. They mainly depend on the process of vibrating sounds with a particular accent. It is a great science, and due to being out of proper use for more than four thousand years, for want of qualified brahmanas, such performances of sacrifice are no longer effective. Nor are they recommended in this fallen age. Any such sacrifice undertaken in this age as a matter of show may simply be a cheating process by the clever priestly order. But such a show of sacrifices cannot be effective at any stage... Since the ultimate aim of life is spiritual realization, the direct way of invoking the holy name of the Lord, as mentioned above, is precisely recommended by Lord Caitanya, and people of the modern age can easily take advantage of this simple process, which is tenable for the condition of the complicated social structure.
¯Srimad−Bhagavatam 2.25.25, 26