Albert Barnes on Acts 18:21

Keep this feast. Probably the passover is here referred to. Why he was so anxious to celebrate that feast at Jerusalem, the historian has not informed us. It is probable, however, that he wished to meet as many of his countrymen as possible, and to remove, if practicable, the prejudices which had everywhere been raised against him, Acts 21:20,21. Perhaps, also, he supposed that there would be many Christian converts present, whom he might meet also.

But I will return, etc. This he did, Acts 19:1, and remained there three years, Acts 20:31.

(b) "Jerusalem" Acts 19:21, 20:16 (c) "if God will" 1Cor 4:19, Jas 4:15