Who should participate?
The scripture is clear that there is one law for all people: His law is for everyone. (Ro 3:19) Yet many argue that these festivals are only for Jews since, for example, God commands those who participate in Passover to be circumcised. (Ex 12:48) But Gentiles certainly may become circumcised and therefore legitimately participate. (Nu 9:14)
Yet some argue further that Paul forbids Gentiles to be circumcised, which may be understood as a proxy for conversion to Judaism as a means of salvation. (Ga 5:2-4) Paul may also have recognized that abstaining from this rite in every respect was needful to ensure clarity of the Gospel for the people of that era. This prudence from Paul during that time period should not be generalized to a universal annulment of the Law for Gentiles today. It seems clear from the Pauline instructions to the Corinthians, who were largely Gentile, that he intended for all of them to keep Passover together. (1Co 5:7-8)