. . . All Protestant churches accept the doctrine of “Sola Scriptura,” the Bible as the SOLE source of authority for believers. Although Protestants voluntarily submit to denominational and pastoral authorities and written statements of faith, they all believe that if these human things (pastors, statements of faith) etc. are in conflict with the Bible . . . they are free to leave that church and seek another with no danger of loss of salvation.
All of the things that the Catholic/Orthodox church believes . . . you can probably find a Protestant denomination that will accept these doctrines, or at least some of the doctrines . . But you will never find a Protestant church that accepts the Authority of the Pope, the Magisterium, or Sacred Tradition. This is THE difference between Protestants and Catholics/Orthodox.
Also, it will help you in your discussions with Protestants if you are aware that there is a LOT of serious objection among Protestants to the incredibly large numbers (33,000) of denominations that Catholics claim. At least one Protestant extra-church organization has broken it down into about 80 denominations. Another claims about 350 denominations.
The problem arises from the “non-denominational,” “free,” and “home” churches, which each have their own statement of faith. To the Catholics who claim such large numbers of denominations, each of these churches is a separate denomination. But Protestants protest vehemently against this definition of a denomination, with good reason. Many of the home churches especially only include a few members, perhaps just one family. So to call them a separate denomination is kind of stretching it.
I would say that “non-denominational Protestant” should be just one denomination, even though they all have slight differences in what they believe. But . . . most non-denoms fit in with some established denomination; the people who belong to the non-denom just want to be free of any central authority (often so they can keep their pastors and their money in their own church . . . So be careful about the large numbers. It suffices that there are at least 80 denominations, which is still an awful lot of “true churches.”
One more thing: to the Protestant, the large numbers of denominations is not bad, but good. They believe that it is through denominations that God works in individuals . . . We have a choice of denominations to help us find OUR place in God’s Church, the place where we can learn the most and serve the most. So if you try to argue that splitting into denominations is a bad thing, most Protestants will disagree with you . . .
Also, Protestants do not see “the Church” as having anything to do with their salvation or their relationship to Jesus. The church is just the place to go for fellowship and teaching. It’s your “Christian family,” . . . And although some of the mainline Protestants have some of the sacraments (Communion, Baptism, Confirmation, Marriage, Anointing with oil for healing), they do not feel that these Sacraments are vital for our salvation and our sanctification, as Catholics do. Keep all this in mind when you talk to Protestants. The very idea of a “mother” church is totally foreign, even idolatrous, to Protestants . . .