Kṛte yad dhyāyato viṣṇuṁ tretāyāṁ yajato makhaiḥ (SB 12.3.52). Tretāyām means the next millennium. That is... It was recommended that people should perform sacrifice.
Tretāyāṁ yajato makhaiḥ dvāpare paricaryāyām. Dvāpare means the next millennium. That is recommended for temple worship, temple worship. The temple worship... So many temples, thousands and thousands of temples, you will find. Not only in India, in other parts of the world also. The churches are also temples, the mosques are also temples, the synagogues are also temples. So this temple worship was introduced in the third millennium.
Now this is the fourth millennium. In the fourth millennium, the Bhāgavata says that kalau tad dhari-kīrtanāt: "At the present moment we have to perform sacrifices by chanting the hari-kīrtana, the glorification of Kṛṣṇa." This is yajña. Other yajñas, although they are prescribed... Because when Kṛṣṇa was speaking, He was speaking generally, but there are specific considerations. This yajña recommended in the Bhagavad-gītā, brahmārpaṇaṁ brahma, brahma havir brahmāgnau brahmaṇā hutam... Now, where is the fire and where is the clarified butter and where is the expert performer of yajña? The performer of yajña must be so much educated.