'But I will tarry at Ephesus until Pentecost, for a great door and effectual is opened to me, and there are many adversaries.'
On the other hand things were going so well at Ephesus, in spite of the opposition there, that he felt that he must stay there until Pentecost. There was a huge opening there, and they were being very effective through the power of God. He wanted them to understand that his visit was being delayed for good reason. He was not his own master. Perhaps too there is the hint here to the Corinthians of how God is with him and working through him, proof of the evidence of His Apostleship.
‘Until Pentecost.' The Jews celebrated Pentecost in late May or early June, so Paul probably wrote 1 Corinthians in the spring of the year (compare 1 Corinthians 5:7; 1 Corinthians 15:20). The fact that he refers to Pentecost demonstrates that he expected the Corinthians to have some awareness of Jewish feasts, especially those connected with great past events for the church, such as Pentecost when the Holy Spirit so vividly revealed Himself to the early disciples, and through them to Jews of many nations who became Christians forming the first infant church (Acts 2).