I do hereby conclude: When the Western Church fissiparated in the sixteen century, the Reformers took a portion of the essential patrimony of the Church with them, and they thereby left both the Roman Church and themselves the poorer for it.
The ferocious debate in seventeenth-century France between the Jesuits and the Jansenists itself points out how much the issues that (supposedly univocally) divided the Reformation from the Church of Rome also raged inside the ancient precincts of the Church. The Jesuits ultimately won out over the Jansenists (often by tarring them as crypto-Calvinists, a charge they found difficult to counter), although the Jesuits’ victory proved Pyrrhic in their case. For Blaise Pascal took the side of the Jansenists and hurled a polemic against the Jesuits in his Provincial Letters so ferocious that it inflicted on the Society of Jesus a wound that, because it was left unaddressed, eventually led to the suppression of the Order by Pope Clement XIV in 1774. The Order was restored in 1815, at which point my story shifts. The odd twist in the plot is that the Catholic Church in the nineteenth century–especially in France–represented a kind of subterranean Jansenism fused to a bourgeois “ledger morality” of Do’s and Don’ts. It was in this hothouse atmosphere that Ste. Thérèse of Lisieux was raised. Although brought up in a thoroughly Catholic household, and pious to an almost preternatural degree, she was assaulted toward the end of her short life (she died at the age of 24 of tuberculosis) by fierce temptations to atheism, which she could only resolve when she came to these “Lutheran” insights, four months before her death:I am very happy that I am going to heaven. But when I think of this word of the Lord, “I shall come soon and bring with me my recompense to give to each according to his works,” I tell myself that this will be very embarrassing for me, because I have no works. … Very well! He will render to me according to His works for His own sake.And in her Offrande à l’Amour miséricordieux, she prays to Jesus thus:In the evening of this life I shall appear before Thee with empty hands because I do not ask Thee, Lord, to count my works. All our just acts have blemishes in Thine eyes. Therefore I want to wrap myself up again in Thy justice, and to receive from Thy love the eternal possession of Thee Thyself. (All emphases added.)Sometimes, when I’m in an impish mood with the seminarians in my class, I like to quote something out of character from someone famous and have the students guess who said it. When I read these quotes from Thérèse, they’ll take a stab and say it’s from Martin Luther in one of his more pious moods, or John Calvin, or maybe Karl Barth. Imagine the shock when I tell them it came from that “Lutheran Carmelite,” the Little Flower!
One of the problems with Protestantism is the tendency to division, but not because of heresy (in the sense of the "revelation" of some other truth). Rather, it is because each person takes a splinter of the whole truth and sets sail upon the sea of life astride his own little splinter. At first, other people will get on the splinter, and then suddenly, one of them finds a splinter of the splinter that appeals to him even more, and he sees that as the entire truth and sets forth on his own little splinter-borne journey. And so forth.
The Protestants didn't really take anything away from the Church, although their overemphasis of their particular splinters of the truth led to a defensive reaction that resulted in closing the mind of the Church to many things that were actually in the process of being worked out.
What Protestants always overlook is that the development of doctrine is a long and complicated process, and the person who is unfortunate enough to have to preach the truth can expect to suffer for it. Many of the people the Church reveres as saints today were, in their time, condemned and even excommunicated. Even Athanasius found himself fighting for the truth alone. But they remained part of the Church, patiently speaking the truth as the Holy Spirit revealed it to them in accordance with tradition, obediently accepting correction and even silence, because they did not have the arrogance to think that their splinter of the truth was the only one.
They were also confident in the truth, confident in God's power to reveal the truth, and confident that if they were right and what they taught came from God, the Church would accept it. They were absolutely right in this, and instead of their truth becoming a separate truth or shard of the truth, it became part of the Church's deposit of truth shared among all believers.
To me, a heresy would be something like Islam, which takes a few scraps of Christian imagery, a few scraps of Jewish ritual law, and a few bits of paganism and creates an entirely new and awful belief system.
Protestants do not do that; I would say that what Protestantism does is take a truth, and emphasize that truth to the extent that it becomes much bigger in the scale of Christian belief than it should be. And then as a reaction to this overemphasis, another Protestant might take an opposite approach (I'm thinking of Protestant struggles over grace and free will, for example), which then will lead to another division and another attempt to constitute a partial truth as the foundation.