Q. 1. To what extent can non-Catholics participate in the celebration of the Holy Mass?
A. 1. Non-Catholics can participate in every part of the celebration of the Holy Mass with the exception of receiving Holy Communion. Such is reserved for Catholics only who have learned to appreciate the Real Presence of Jesus in the Eucharist.
If non-Catholics only want to observe the Catholic liturgy, they should stand and/or sit when the faithful stand and/or sit (and kneel). Allowing non-Catholics to observe the Catholic liturgy often ignites sparks of graces that brings about the conversion of the non-Catholics.