There Is Not A Single Truth In Protestantism That Does Not Exist in Catholicism

The Reformation Wall William Farel , John Calvin, Theodore Beza, and John Knox.

Which is the divine religion established by Jesus Christ? Is there one, or are there many such? Are there several religions which may equally be the Church of Christ? We have among us Episcopalians, Presbyterians, Baptists, Methodists, Lutherans, Catholics. Are they all right? Are they all wrong?

I must confess that to me it is painful to see so many claimants. I know so many people of different denominations whom I esteem that I hate to believe that their belief is not right. Here let me say a very important thing. In considering this matter, we must distinguish between the man and his creed. A man may be personally sincere, yet his religion may be wrong; in condemning his religion, we do not condemn him. On the other hand, his religion may be true, yet he may be personally a very bad man. We see this in various other matters. 

For instance, in politics, a Republican may denounce the Democratic party, yet esteem the individual Democrat. I know a Democrat who spent most of his energy denouncing Republicans, yet his own son and his best friends were Republicans. You may condemn suffragettism, yet admire and esteem the individual suffragette, and vice versa.

So in this vital matter of religion, we have the greatest consideration for the individual

who may be in error, but for the error itself we have no tolerance. Christ Himself sets us the example in this by His love for the sinner, although He hated and denounced sin. In considering the various religions, we shall demonstrate that there is but one true religion, the others being consequently not true. But individuals in those others may be sincere, and if in the sight of God they are doing all in their power to live as God wants them to do, they are in a certain sense in the true Church, though not specifically so.

A man may be nominally a Socialist, yet his life and conduct might be altogether at variance with the logical platform of that party.

So a person may be of a religious denomination which is false, and yet live superior to it. Cardinal Newman, who had the experience, said that a Protestant was, as a rule, better than his religion. I myself have received many persons from various denominations into the Catholic faith, and I have often found that at heart they were Catholics all along. By this I mean that, although Protestants, they were acting on Catholic principles, without knowing it.

All the great saving truths of Protestantism are what were carried into it from the Catholic faith. There is not a single truth in Protestantism that does not exist in Catholicism. I say not a single truth, for you will find that everything that is absolutely true in every religion of the world is in the Catholic religion, — only without any admixture of error. 

Link (here) to the book God and Myself by Fr. Martin J. Scott, S.J.