transhuman is correct, I think. They figure his death matters, but his resurrection is incidental to the whole thing. In this, as in so much else, they are teaching something more nearly the opposite of the gospel.
rattigan has neatly missed the point: from the very earliest days, the Lord's Day was the Sunday communal feast. It is an indisyncratic and historically absurd idea that leads one to suppose that the mandate to celebrate the Eucharist was designed as a replacement of the Passover only and, thus, only to be done one time each year.