Is it a sin if a Catholic see mass in a non-Catholic church?

Answer 1

It is a sin for a Catholic to participate in a non-Catholic Church service.

Non-Catholic perspective

There are many Catholics who regard anything else apart from their particular branch of Catholicism as wrong, and are therefore, necessarily, as guilty of almost cultic attitudes as, say, Jehovah's Witnesses who regard any other thinking apart from their own as the work of satan. Many of these Catholics forget the reasons for the Protestant Church's formation in the first place; corruption within the Catholic Church and the adoption of non-scriptural beliefs and practices that have been invented by man - transubstantiation and the veneration of inanimate bread and wine as the actual body and blood of Christ as another.

The names 'Catholic', 'Anglican', 'Methodist', 'Baptist' and any other Protestant division, are all man made. Therefore, whilst in the sight of the Catholic Church participation in a non-Catholic service may well be seen as a sin by some individuals, in the sight of God it is certainly not. Scripturally, and adhering to Christ's teaching, and the Word of God in Paul's letters means that simply standing up and professing 'Jesus is Lord', and meaning it, makes one a Christian whatever man-made label is given and therefore attendance at and/or participation in any Christian service in any denomination by either a Catholic or a non-Catholic, will receive God's blessing, despite what those in the Catholic Church hierarchy, or those who have been tutored and indoctrinated in the Catholic Church doctrine, might say.

ANSWER (by a Catholic):

The Catholic Church forbids Catholics to receive Communion in non-Catholic churches. Likewise, the Catholic Church forbids non-Catholics to receive Communion in the Catholic Church. Hopefully, someday we Christians will be able to unite on the theological issues that divide us and return to what Our Lord intended -- one Lord, one Faith and one Church.

Most Catholics don't believe it is a sin to attend a non-catholic worship service, ie on Sunday morning, but some might say that a Catholic should also attend Mass. Attending a non-Catholic worship service does not excuse a Catholic from his Sunday obligation (or other Holy Day).

Attending a non-Catholic worship service is, in my opinion, a learning experience and fine. Some Catholics believe it would not however, be okay for a Catholic to receive communion in another Christian church because some would see it as dishonest as Catholics and non-Catholic Christians do not believe the same thing about communion. Protestant communion (including Anglican) is not the same as Catholic communion and we are not permitted, as Catholics, to join in because some Catholics do not regard it as valid. Therefore some would say that it is dishonest to pretend.