~Why does one have to be orthodox? Are not protestants and other people holy?~
I love this question. Here are a few points.
1) To be orthodox means that one is obedient to the Teaching Magisterium in the Church. Obedience and humility are marks of true holiness. If one is disobedient, one is not only sinning, but possibly having many hidden sins from which one needs to repent and leave behind.
2) The road to perfection illuminates the conscience and releases the gifts of baptism. This means that a person on the road to perfection is being purged of false ideas, such as heresies. For example, many protestants see nothing wrong with contraception because they have not understood or prayed about the beauty of the teaching of the Catholic Church. Again, this sin and the tendency to sin would be purified, which means, a person would most likely convert to Catholicism. Other problems, such as not believing that the Eucharist is the True Presence, is a serious impediment to being united with God.
If a protestant knows that the Church's teachings are true and still does not convert, that can indicate a sin against the Holy Spirit: knowing the Truth and not acting on it.
3) The road to perfection is the road to the heavenly union with God in the Beatific Vision. All people in heaven are Catholics! They have come to know the Truth in the fullness of Truth. Thankfully, we have purgatory not only for punishment, but for purgation.
4) Holiness requires a saying yes to the call of God. It requires sanctifying grace, found in the sacraments, especially in the sacraments of Reconciliation and the Eucharist. Again, when one denies the efficacy of this means of the life of God, one is placing obstacles on the path to oneness with Christ.
5) Not only is sin purged on the way to perfection, but imperfections. It is almost impossible to see imperfections until mortal sin is gone and venial sin is actively being purged. Some people may be given extra graces by God, in His Will, outside of the Church, but they would obviously convert in the face of Truth.
6) True holiness demands a destruction of the self-will. This is not a common idea among protestants, who think they are saved once and for all and do not need to go through stages of grace. They do not, on the whole, understand grace as we do. I discussed this at length in other posts.
7) Last, but not least, orthodoxy indicates that one has put on the Mind of Christ, who created the Church as an institution and guides it through the Pope. If one is not willing to think like Christ, how can one love Him enough to want to be with Him forever, and thus undergo purification?
P.S. Of course, there are people who did not become Catholics while on earth, in heaven; but now that they are with God, as I mentioned above, they are all Catholics!
