[DouglasKC]

I think the usual reading of "They devoted themselves to the Apostles' teaching and fellowship, to the breaking of bread and the prayers." is generally thought to refer to celebrating the Eucharist. I would say that those who want to assert that the Mass should only be celebrated on 14 Nissan would want to explain how in fewer than 100 years that notion was lost, and how, once lost, it was recovered by the Jehovah's Witnesses and others 1800 years (give or take) later.

Following the Lord's instructions in scripture was never "lost". However there was a movement by the traditional church away from practices that resembled Judaism due to anti-semitism generated by the Jewish revolts of the 1st century. Those who continued to observe the feast days of the Lord Jesus Christ were eventually branded as heretics by those who didn't. The history of those who observe these days isn't prominent for understandable reasons.

But the bottom line (at least to me) it that Jesus observed it on Passover, one of his feast days that was created through him. As Christians, followers of Christ, we should do the same.

[RobbyS]

I think what you are saying only makes sense in the context of when to celebrate Easter. There was a dispute for many years about that. In the end, the decision was to focus on Friday as the day on the cross and Sunday as the day of resurrection. The text itself leaves the matter open.