1 Corinthians 16:8

But I will tarry at Ephesus until Pentecost.

Paul decided to remain at Ephesus until after Pentecost because the cause in Ephesus still demanded his presence. Ephesus had been the center of his work for over three years, where a flourishing church had been raised up. From that center the gospel had spread throughout the province of Asia among both Jews and Gentiles.

He had for some time been planning another missionary journey to pass through Macedonia and Achaia to Jerusalem and then to see Rome. In harmony with that plan he sent Timothy and Erastus ahead into Macedonia, while he himself stayed on at Ephesus. An event soon occurred which hastened his departure from Ephesus.