Nol de Hartog is sometimes also called ‘the resilient Christian’. With his ideas he stepped outside of the common orthodox thinking, which caused opposition from several sides. His Christian colleagues and fellow theologists reproached him for stepping too far outside the official teachings. He had to refute accusations. Next to that he did not shy away from debating with the leaders and the representatives of the workers movements. And not only with them.
During a protest meeting in the old RAI building, against the emerging nazi’s and NSB’s he shared his thoughts about life. His son, the well-known writer Jan de Hartog, writes about this in his book ‘Memories of my mother’:
Even now, after so many years, people still address me about it: “Once, a long time ago, before the war, I heard your father speak (…)” I cannot remember a single word myself from what he then said. (…) But that night I discovered that his courage was authentic (…), I realized that he meant what he said: that being a Christian indeed meant you should be a hero. At least in his case. (…) The fact remains that my father’s deed was in accordance with his conviction and that he himself did what he told others to do in his sermons. 
Ánd if all this was not enough : … When it was tried to prove scientifically that God does not exist and the association “The Dawn” was founded, de Hartog founded as a counterweight “The Summit of Noon” in which he stood up for Christianity and the church.
A resolute, aroused and also inspiring man, who tried to fathom life and really took his responsibilities very seriously. De Hartog graduated in 1903 cum laude as a doctor in theology, with the subject: ‘The problem of will-freedom in Schopenhauer.” It was very special for his time that he noticed relations between philosophy, religion and science, and also that he made comparative studies of religion and culture in the International School of Philosophy. His versatility is apparent from the choice of literature, poetry and music that he quotes and integrates in his work. In 1915 he published an anthology of the work of the German philosopher Jacob Boehme (1575-1625), in the series Hours with …. Books of wisdom and beauty. In the prologue he quotes Boehmes famous words:
For whom time has become as eternity and eternity as time, he is liberated from all struggle. 
Just like Boehme, de Hartog encountered conflict and opposition in his life, and maybe he recognized himself in those words. In his book ‘The meaning of our life’ he further elaborates on this subject. He writes:
We have to die, but the true dying is self-surrender as to the spirit, from which is born the secret that Boehme refers to as follows: ‘He or she who dies before he dies, will not perish when he (she) dies.’ 
De Hartog puts the spirit, or God, opposite to nature. By doing so he does not mean that nature would not be realized through the divine spirit, but that a human being must leave behind the lower reality in order to be able to enter into the higher reality.
A human being is the turning point in the all-phenomena. The natural order of self-maintenance and egocentricity must change into the spiritual order of self-surrender in love. To break with the natural instinct means no less than becoming partakers in the spiritual aptitude and through this sanctifying the natural instinct. (…)
Thus, the human being travels through the desert of nature towards the promised land of the spirit, and ascends from the lower valleys of the time-spatial, material turmoil up to the high plains of the eternal, spiritual exempt. 
De Hartog has written many books, most of which have been forgotten. But his thoughts were recognized by two brothers, Wim and Jan Leene. Until 1917, De Hartog was a preacher in the Large (Groote) or St. Bavo Church in Haarlem. The brothers participated in every of his services. But it was clear that De Hartog did not wish to have followers; according to his opinion, every human being could as to his or her own insight be an independent, strong Christian, with a firm belief and reasonable persuasion.
His vision provided an answer to the brothers to the question of existence, the relation between spirit and nature, God and man. Through him they found the first source of which everything emanates: the point where the divine spirit touches a human being. The source that is in the most inner being.
The two brothers continued on with the principle of God-in-the-human being, that De Hartog placed so clearly and realistically before them, and also the idea of the twofold-ness which is everywhere, in the world, in the universe and within mankind. All this led to their concept of the two nature-orders.
So we can read in The Egyptian Arch Gnosis:
Of all creatures of nature only man is twofold, as Pymander establishes. On the one side there is within the human system the grain of seed of immortality, the spirit spark, also indicated as the rose of the heart; on the other side there is the mortal human being, the natural being. You cannot find a single other creature of such a twofold nature. 
No matter which sacred language came to their knowledge , they recognized this basic thought and started in their turn to inspire people. They re-connected the people with the ‘universal teachings’ of all times.
How true are the words of Arnold Hendrik de Hartog:
This is the grandness of a human life, that it is a world in itself which, also when it has disappeared, leaves its richness as a heritage for those who as seekers try to grasp the same knowing. 
Arnold Hendrik de Hartog was a Dutch-reformed theologist, preacher and professor.
In 1906 he married J.L.G. ( Lucretia) Meyjes. She wrote the book ‘Hidden paths’ and she also translated from German; she felt connected with the ideas of the Quakers. She was a teacher at the International School of Philosophy in Amersfoort, founded in 1916, among others by her husband. From 1926 till 1930 De Hartog was professor by special appointment in the apology of Christianity, at the Theological Faculty of the University of Utrecht. At the end of 1930 he was appointed professor in philosophy at the department of religion and ethics at the University of Amsterdam.
Unity is the essence of life and spirit. Life and spirit meaning more than just bonding together, yet, they manifest themselves in joint bonding.(…)
Death has not arrived in the world through sin, as to the outer aspect, but as to the inner aspect: mankind shying away from the spirit of life, which is from God.(…)
Thus we are driven into darkness, where – still – the Eternal speaks! Into the heart! 
Being moved by the eternal Movement the light bearer now moves forward spreading his brilliance in time, the world and humanity. This steadfastness in the heart of eternity, this “firm spirit” of radiance, is the incorruptible good that has become to them who passed through death, the death that quenched the earthly light, so that the heavenly light might shine. 
In mankind, matter and spirit, higher and lower nature are married, so that man may find between the two the treasure of heaven in the earthen vessel! (…)
As a personality, man transcends the natural, instinctive, unfree life and celebrates the freedom of the mind, where he breaks with natural impulse, instinct, passion and elevates himself. (…)
His personality is all-encompassing as to nature and all-conquering as to spirit. 
What unconsciously dreams in the spatiotemporal manifestation: the secrets of the mineral kingdom, the jubilant rise of floral scent and color, of plant, blossom and fruit, the graceful mobility of the animal kingdom, all this comes to its consummation in human consciousness and there it becomes the praise of the Eternal. The human kingdom must establish the kingdom of peace through the descent of divine love.” 
In the name Jesus Christ there are two meanings: the turning of God to man and the ascent of man to God. (. . )
The universal Christ signifies the invigorating spirit, the divine principle of the new birth, the heavenly descent, descending and procreating in the lineage of the children of men. (…)
The Son of God became the Son of Man, so that man might become the Son of God. (…)
The Christ revelation in Jesus Christ, the cycle of his birth, death, resurrection, ascension, is repeated in his own, continued, carried on as a motive force, as a target of compassion, which stems from the divine love of the father in the son, of the son in the spirit, of the spirit in the reborn humanity. Thus closes the wedding ring of eternity. 
The Scripture shines forth from the eternal heart of truth into the heart of the God-seeking and finding human being. The Scriptures contains, as Mrs. L. de Hartog-Meyjes stated in the preface to her diary ‘Hidden Ways’: the history of the human heart, which finds God. (…)
The word of God shines like an everlasting lamp in the secret sanctuary of the heart of man reconciled, redeemed, and glorified; and at the same time this word shines over the wide sea of temporality like a radiance of eternity. 
 De Hartog, J., Herinneringen aan mijn moeder [Memories of my mother], pg. 27-28, Atlas Contact Amsterdam
 Ibid pg. 113
 De Hartog, A.H. Uren met Jacob Boehme [Hours with Jacob Boehme, a selection of pieces from his works], pg. 7, Hollandia Baarn
 Ibid pg. 7, Hollandia Baarn
 Ibid pg. 46, Holland Amsterdam
 De Hartog, A.H. De zin van ons leven [The meaning of our life], pg. 162 en 175, Holland Amsterdam
 A.o. The Egyptian Arch Gnosis, The Chinese Gnosis, the Nuctemeron of Appolonius of Tyana, Rozekruis Pers Haarlem. Rozekruis Pers Haarlem
 Huijs, P,, Geroepen door het wereldhart [Called by the World Heart], Cited from A.H. van den Brul: ‘J. van Rijckenborgh – modern rosicrucian and hermetic gnostic’, in Pentagram, 17e year, nr. 2, Rozekruis Pers, Haarlem 1995
 De Hartog, J., Herinneringen aan mijn moeder [Memories of my mother], pg. 113, Atlas Contact Amsterdam
 De Hartog, A.H. De zin van den dood [The meaning of death], pg. 11,12,13, 1930
 De Hartog, A.H. De zin van ons leven [The meaning of our life], pg. 56, Holland Amsterdam
 Ibid pg. 13 and 59
 Ibid pg. 37 and 55
 De Hartog, A.H. Christendom, [Christianity] pg. 134, 137, 138, 172, 1922
 Ibid pg. 66 and 67