In first Corinthians 5:7 when Paul says to keep the feast (Passover) it is a metaphor. The context deals with sin that was in the midst of the Corinthian church, namely fornication.
Under the Old Testament the Israelites were to put away leaven for seven days and to eat unleavened bread only. This was a type of the putting away of sin in exchange for purity.
According to the context of 1 Corinthians 5, Paul says nothing about the feast of Passover which was to be kept on the 14th day of the month Nisan (the first month on the Jewish calendar). He does not make reference to a day as Passover, as the Old Testament did. (see Ex 12:6,14,18,19; Numbers 9:2; 28:16; Deuteronomy 16:1; Joshua 5:10; Ezekiel 45:21)
Leviticus 23:5 says, In the fourteenth day of the first month at even is the LORD’S Passover.
Paul does not refer to Passover as a time on the calendar, or a ceremonial festival when speaking to the Corinthians. On the contrary, Paul refers to Christ Jesus himself as our Passover.
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: 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. (1 Corinthians 5:7-8)
Paul applies the object lesson which was contained in the shadowy type – the Passover given to Israel – and tells the Corinthians to walk in the reality of it. In other words, Paul says, Put away this sin from your midst and serve God in Christ with sincerity and truth because Christ, who is our Passover, was sacrificed for you.
There is nothing wrong with dedicating the Passover season as a time for the Lord to focus on Christ’s death for us. In fact that is a very good practice. The error comes in when the festival becomes a law for Christians to observe as is becoming more of a common place within some of the modern day Messianic movements, such as the Hebrew Roots Movement.
The new testament writers are the authoritative interpreters of the old testament scriptures and they gave us everything we need to know for godly and righteous living.
That which was foreshadowed in the feasts has become reality in Christ Jesus, and we can walk in the reality every day because the light has come and the shadow had been put away.