CC Ādi 7.160
vṛndāvane pāṭhāilā śrī-sanātana
After thus delivering the people in general, the Lord desired to leave Vārāṇasī. After instructing Śrī Sanātana Gosvāmī, He sent him toward Vṛndāvana.
The actual purpose of Lord Caitanya’s stay at Vārāṇasī after coming back from Vṛndāvana was to meet Sanātana Gosvāmī and teach him. Sanātana Gosvāmī met Śrī Caitanya Mahāprabhu after the Lord’s return to Vārāṇasī, where the Lord taught him for two months about the intricacies of Vaiṣṇava philosophy and Vaiṣṇava activities. After completely instructing him, He sent him to Vṛndāvana to execute His orders. When Sanātana Gosvāmī went to Vṛndāvana, there were no temples. The city was lying vacant like an open field. Sanātana Gosvāmī sat down on the bank of the Yamunā, and after some time he gradually constructed the first temple; then other temples were constructed, and now the city is full of temples, numbering about five thousand.