My understanding is that God created certain days for us to celebrate and honor him. These days are outlined in Leviticus chapter 23. God, being perfect, also knew that these days would apply when, and after, his first born son was sacrificed on the cross for us. These days are markers and outline God's salvation. That's why Christ celebrated Passover and all the other festivals ordained.
For example, Passover in the OT clearly pointed to the sacrifice of Christ on the cross "our passover". However, Christ changed the symbols and said we were to celebrate it as a remembrance of him (Luke 22:19, 1 Cor 11:26)
The Days of Unleavened Bread represent new Christians, those who have accepted Christ, as coming out of sin, spiritual Egypt. Leaven is a symbol of sin and removing leaven teaches us that we are to leave sin behind.
Pentecost represents the formation of the new testament church.
These harvest festivals took place in the spring. We are now in the long summer in God's prophetic calendar. The fall festivals start with the Feast of Trumpets, which symbolizes the return of Christ, at the "last trump" (1 Cor 15:52). The day of atonement pictures the putting away of Satan and the feast of tabernacles pictures the millenium reign of Jesus Christ.
I've greatly simplified these, but this is the gist. God doesn't create in vain and he didn't create holy days only to have man ignore them.
God doesn't create in vain and he didn't create holy days only to have man ignore them.
So why weren't the NT Gentile christians commanded ... or even encouraged ... to keep these days ?
There is easily a much stronger argument from the New Testament ... that it doesn't matter what special days one keeps ... than that it does.
There are twenty-one books of christian instruction from the Apostles in the New Testament. Though these are full of doctrine, encouragement, and command as to the specifics of christian living, ... the keeping of special days is almost never mentioned, ... and then not positively (i.e. as regards specific days to be kept).
My take on New Testament teaching is that it majors on the maturing and conditioning of the heart, ... rather than the keeping of any external practices.
Paul says that the christian's focus is to be love.
If one lives within the context of abiding in ... and the sharing of ... God's love, ... then one will be sure to be carryng out the will of God for one's life.
Keeping the Law is Old Testament stuff ... it only served to bring us to the knowledge that we need the Saviour.
Once we have come to the Saviour and have made our peace with God, ... we are free to live our christian lives as we are led by His Spirit, ... and according to the higher principle ... of God's love.