Next to that it was a Prof. Opzoomer, who educated him in the scientific method. And so the disintegration of the unitary Bible as the presumed Word of God, came together with a new attitude of critical inquiry. Thus in 1852, as a 21 year old, he wrote a book review that was to be published in the Annals of scientific Theology (Jaarboeken voor wetenschappelijke Theologie) in 1853. In it, the emerging battle of these developments takes form, in which for now he retains his religious posture, but clearly with an open mindedness and inquisitiveness which prefigured his later development. Later, at the University of Leyden, it is a Prof. Scholten who further forms him in the scientific method.
In his 1854 doctoral dissertation de Realismo et Nominalismo (Latin was still the tongue of the scholarly world in Europe), he lays the ground work for much that was to develop later, though the thinking is still clearly immature. He then becomes a reverend at Leuven, where he stays till 1857, having a mixed constituency which required him to preach in French, Dutch, and English, and the denominations were equally mixed in his flock, ranging from Anglican to every other Protestant variety, set amidst a very Catholic surroundings. Amidst all this he continues to nurture his analytical scientific mind while retaining a backbone of deep religiosity, yet he evolves towards an empiricism which is not accepted by the religious dogmatism all around him.
Then in 1856 appears an article from his hand "Historico-critical principles. Introduction to some psychological study of the Gospels" (Historisch-kritische beginselen. Inleiding tot eenige psychologische studiën over de Evangeliën.) With this publication he moves decisively into the vanguard of critical theological thinking of his day. By this time he is moving from the confines of Leuven (Louvain) to the more cosmopolitan, mercantile world of Rotterdam, from October 1857 to March 1865. Circa 1860 in his parlance "Israel" is the name of the religious people everywhere, in a symbolic sense, and his regard for the Bible is still always evident, despite his critical approach. He continues to advocate that his increasingly modern and pluralistic theology does have a place in the Protestant Church, but a few years hence he will resign his function. Clearly his evolution in a very critical direction remains rooted in the deep religiosity of his heart, and the traditions in which he was raised. He abandons theological dogma without abandoning his love for the Bible.
In 1865 he finally resigns as pastor of his congregation in Rotterdam. He stays for another year and a half but then moves to Heidelberg, to a villa outside of town with the name of Intermezzo. To him now traditional Christian faith can no longer be reconciled with modern philosophical inquiry. He leaves the church-bound life of which he was such an active part, always drawing a full house in spite of his being increasingly "far out" for his day. After some time he wrote a 40 page pamphlet to account for his leaving his professional position in Rotterdam "To My Last Congregation." In Heidelberg he writes a four volume history of Catholicism, notably he still feels that the essence of moral religious life is still easier within the church than outside of it. He becomes a Professor in Heidelberg. Eventually he gets an official blessing from the faculty to pursue his liberal insights, and as a full professor from 1870 on he teaches more history of religion than theology. By 1877 we find him in Amsterdam.
Notably in an 1871 article he develops a position, which he seems later to have renounced again, when he arrives at the following conclusions - I translate the summarization in the book by Naber (see below):
...Thus we should arrive at the criticism of that mode of thought [naturalism] and its core: the conviction of the objectivity of sensory perception. That criticism is of a physiological nature. What man observes is, according to newer theory, always the product of his mind, a product to which nothing objective outside of us is the cause, except for the movement of a certain medium; and in this connection it should be admitted promptly that the proposition of movement as much as of the moving medium is again our own creation. We could call this teaching properly physiological idealism. The world, as we see it, does not exist outside of our consciousness. This position does not rest on any a priori idealism, but exclusively on an analysis of the functioning of our senses; and whoever does not grasp the truth of this statement, is not lacking in philosophical development, but simply in physiological knowledge. A critique based on pure physics, after all physiological, of the working of our senses allows us to maintain the independence of the human mind in a way which forever robs materialism of its scientific character. From this point of view every law of nature becomes a law of the mind; in other words: succession of natural phenomena should be labeled an association of mental images. Het notion of cause disappears, to make place for the recognition of the objective identity of those appearances, among which we earlier assumed a causal connection, and for the determination of the sequence of events, behind which I have to imagine the force that is always identical to itself. Exactly because of the study of physics, the spiritual comes into its own: the sensory world the deed of the independent mind; that which science can recognize in the world the purely abstract, after all mathematical. Next to these two great outcomes materialism seems badly dated. The contradiction of naturalism and supernaturalism fades away. No longer is metaphysics dependent on physics. In one word, we refuse to find objective reality in the empirical world. ...In other words, here Pierson refutes Dr. Samuel Johnson's refutation of Bishop Berkeley. The nerves that hurt when he kicked the rock, were themselves part of the perceptual universe, which merely tautologically validates itself, proving nothing. While Pierson later backed away from the stark purity of these observations, even though he retained the essence of it in other ways, it should be interesting to the reader today, that he has prior Quantum Physics, and prior to the appearance of A Course in Miracles, arrived at a metaphysical position, which given his learning at the time (having taught history of religion at Heidelberg), hews closest to Advaita Vedanta. Unsurprisingly, this 1874 article was not taken graciously by the world around him.
In his four volume "History of Catholicism" which was complete still at Heidelberg he gets to the question if Peter really founded the Church. He takes to the subject a studied objectivity in which he likes some things and not others, and finds simple that Protestantism works better for some than for others. He cannot help but note that the Catholic Church has been more constant than Protestantism which, then three centuries old, has dissipated itself in unending schisms. Here is where it really gets interesting: Pierson writes (as cited by Naber):
If it had really been the intention of Jesus to found a world religion, he would have merely shown a sad lack of understanding of the human condition. A religion which preaches only one thing: God is spirit, and the fulfillment of the Law is to love Him above all else, and our neighbors like ourselves, a religion without metaphysics, and without worship, such a religion would have been suited to the overwhelming majority of our kind... A child could believe it! ... of the early church fathers he bemoans a lack of mystical orientation, and the fact that so little of Christianity is a religion, and so much dogma.Pierson ends up feeling that the Catholic Church in the end mostly maintained its relevance by eventual adoption of all the things it fought at first, something that is still true in our time with the budding Catholic Bible scholarship, which emerged since Vatican II, among other things. What may be most remarkable is the sense of balance which Pierson brought to his topic, such that Protestants could not love his book.
From 1874 to 1877 Pierson lived in Utrecht, before finally becoming a professor at the University of Amsterdam. For now I'll leave the story here, to be completed some other day. Pierson was to become a founding father of Dutch Radical Criticism (German: Radikalkritik) when he finally evolves to a position that breaks with Christian main stream orthodoxy in questioning much of the work of Paul. This is also my reason for discussing it on this site - the critical questioning of Paul by this group of scholars also lays at the foundation of J.W. Kaiser's feelings on the topic, likewise the seeds of a more mythological treatment of the Gospel accounts are here.
Note: The above is based on the 1907 book by Samuel Adrianus Naber, Allard Pierson Herdacht (Memories of Allard Pierson)