Matthew Poole and continuators on Acts 18:21

21 But bade them farewell, saying, I must by all means keep this feast that cometh, in Jerusalem: but I will return again unto you, if God will. And he sailed from Ephesus.

The Feast of the Passover; which is meant where Feast is put absolutely, unless some after expression qualifies it: not that this holy Man did out of Conscience to the Feast, intend to observe it; for Christ is the end of the law to them that believe, Rom. 10.4. but because of the vast concourse from all places to Ierusalem at that time; which would give him an opportunity of making Christ known to such multitudes, and to gain their Souls unto him.

Tho he was an Apostle, and had the Spirit of Prophesie, and might know whether he should return or no; yet he does not absolutely promise them to return to them; but conditionally, if the Lord will, to teach us what caution we should use in all our Promises and Resolutions, as Iam. 4.15. being we know not what a day may bring forth. Besides, in our owning of Gods Will and Pleasure, we acknowledg a Providence of God in all things, especially in our concerns; which we desire to refer all unto.

Marginal references: 1 Cor. 4.19. Heb. 6.3.