Acts 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.
Jesus kept all of the old feast days commanded by God and taught the apostles to do the same. Then He sent them into the world with this command.
Matthew 28:19 Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost: 20 Teaching them to observe all things whatsoever I have commanded you: and, lo, I am with you always, even unto the end of the world. Amen.
The only feast day that really remains after Christ’s death and resurrection is Passover. No other feast days were instituted. God’s statement of man made feast days still stand. We could go into the pagan origin of many of the current “feast days” but you could easily do a search of the pagan roots of each of them.