Yep, here is Paul leading the Corinthians (a Gentile church by the way) astray...
1Co 5:6 Your glorying is not good. Know ye not that a little leaven leaveneth the whole lump?
1Co 5:7 Purge out therefore the old leaven, that ye may be a new lump, as ye are unleavened. For even Christ our passover is sacrificed for us:
1Co 5:8 Therefore let us keep the feast, not with old leaven, neither with the leaven of malice and wickedness; but with the unleavened bread of sincerity and truth.
Wonder why He did this?
Act 18:21 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.
Why was the Fast ( the Day of Atonement) mentioned here and used as a season marker by Luke?
From Adam Clarke...
"Sailing was now dangerous, because the fast was now already past - It is generally allowed that the fast mentioned here was that of the great day of atonement which was always celebrated on the tenth day of the seventh month, which would answer to the latter end of our September; see Lev_16:29; Lev_23:27, etc. As this was about the time of the autumnal equinox, when the Mediterranean Sea was sufficiently tempestuous, we may suppose this feast alone to be intended. To sail after this feast was proverbially dangerous among the ancient Jews. See proofs in Schoettgen."
When Christ returns, the world WILL keep the Feasts, there will be no choice...
Zec 14:16 And it shall come to pass, that every one that is left of all the nations which came against Jerusalem shall even go up from year to year to worship the King, the LORD of hosts, and to keep the feast of tabernacles.
Zec 14:17 And it shall be, that whoso will not come up of all the families of the earth unto Jerusalem to worship the King, the LORD of hosts, even upon them shall be no rain.
Zec 14:18 And if the family of Egypt go not up, and come not, that have no rain; there shall be the plague, wherewith the LORD will smite the heathen that come not up to keep the feast of tabernacles.
Zec 14:19 This shall be the punishment of Egypt, and the punishment of all nations that come not up to keep the feast of tabernacles.