Philip Yancey says that Jean Nicolas Grou was "a mystic from the eighteenth century, [who] prescribed that healthy prayer should be humble, reverent, loving, confident, and persevering — in other words, the exact opposite of impatient." 
Jean Nicholas Grou was born at Calais, in the diocese of Boulogne. He was educated at the Lycée Louis-le-Grand in Paris, which at that time was under the direction of the Jesuits. At the age of fifteen, he was admitted to the Jesuit noviciate. He made his first vows at the age of seventeen, and was afterwards employed in teaching, according to the custom of the Society. In this employment his taste for literature was developed. He was particularly fond of Plato and Cicero, in whose writings he found, along with a great wealth of style, finer thoughts and a purer code of morals than in the majority of ancient authors. The first fruit of his labours in Greek philosophy was a French translation of Plato's Republic. He went on to translate Plato's Laws and then his other dialogues.
The decree suppressing the Jesuits in France obliged Grou to seek refuge in Lorraine. He lived for several years at Pont-à-Mousson, where he made his final vows in 1765 or 1766. After the death of Stanislas, the Jesuits were also banished from Lorraine. Grou moved to Holland, where he continued his labours on Greek philosophy. He later returned to Paris, where he took the name of Leclaire. At Paris he led a very retired life, dividing his time between his studies and his religious duties. At first the Archbishop of Paris, Christophe de Beaumont, employed him to write upon subjects relating to religion; the Archbishop also granted him for some time a pension, which eventually ceased. A holy nun of the Visitation, whose acquaintance he made through one of his brother priests, and who was believed to be favoured with special graces, induced him to enter upon the way of perfection and a life of prayer. He gave to literary work all the time which was left to him after fulfilling his spiritual exercises and the cares of his ministry. The result of this laborious life was the composition of several books upon matters of piety. His first work of this kind was La Morale tirée des Confessions de Saint Augustin (1786), in which his design was to contrast the morals of Christianity with the systems of unbelievers, drawing his principles from the writings of Saint Augustine. This work was succeeded by Les Caractéres de la Vraie Devotion (Marks of True Devotion, 1788), in which Grou defined what true devotion is, and also its motives, its object, and its means. This volume was quickly followed by the Maximes Spirituelles, avec des Explications (Spiritual Maxims Explained, 1789).
About the same time he also composed several little pious treatises, of which he had copies made for the use of a devout lady of high rank whose director he then was. These manuscripts, which consisted of nine small volumes, have thus been preserved. He had also undertaken a great work which had cost him fourteen years of research and trouble. Before leaving France he confided the manuscripts of this work to a lady, who was arrested during the Reign of Terror, and whose servants burned them, fearing they might compromise their mistress.
The life of Father Grou was upright and peaceful; he was much esteemed, enjoyed a pension from the king, and did great good by his advice and his writings. When the Revolution broke out, he at first wished to remain in Paris and continue exercising his ministry in secret; but the nun mentioned earlier persuaded him to seek refuge in England. He followed her advice, and was invited by one of his former brothers in religion, who was then chaplain to a prominent English Catholic, Mr. Thomas Weld, a member of the recusant Weld-Blundell family and the father of Cardinal Thomas Weld, to come and stay with him. Taking up his abode with the Welds at Lulworth Castle, Grou became the spiritual director of the whole family. His gentleness, his wisdom, and his experience in the ways of the spiritual life, were most useful to the persons who gave him their confidence. It was then that he learnt that his great work, the fruit of so many years of labour, had been burnt at Paris. He bore this loss with much calmness, and said simply, “If God had wished to derive any glory from this work, He would have preserved it.”
He observed, as much as possible, the rule of the Jesuits; rose every day at four o'clock in the morning, without light or fire, made an hour's meditation, said his office, and prepared for Mass, which he never failed to celebrate every day until attacked by his last illness. He practised the strictest poverty, having nothing whatever of his own, and asking with the greatest simplicity for books or clothes when he needed them. He was remarkable for his lively faith and constant tranquillity of soul, as well as his great humility, modesty, and zeal. In 1796 he had printed in London, the Meditations, en forme de Retraite, sur I’Amour de Dieu (Meditations, in the form of a Retreat, upon the Love of God), and also a little treatise called Don de Soi-mēme è Dieu (The Gift of One's Self to God). Some theologians imagined these works contained ideas favourable to Quietism; but a French bishop, after examining them, pronounced them to be perfectly sound, and free from any taint of the kind. Another work of his published in London was The School of Christ, which appeared not in French but in English.
The Supplement to the Library of Jesuit Writers, published at Rome in 1816, mentions also, as written by Father Grou, La Science du Crucifix, (The Science of the Crucifix); and its continuation, La Science Pratique du Crucifix dans l’usage des Sacrements de Pénitence et de Eucharistie (The Practical Science of the Crucifix in the use of the Sacraments of Penance and the Holy Eucharist).
Two years before his death, he had a very painful attack of asthma. Some time after, he was seized with apoplexy and then with dropsy. His legs swelled to an enormous size; he could not remain in bed, and passed the last ten months of his life in an arm-chair. He continued to the very end to hear the confessions of the pious family with whom he lived. Holy Communion was brought to him twice a week. When he felt his end approaching, he asked for the last Sacraments, and received them with full consciousness and great devotion. A short time before he died, holding his crucifix in his hands, he exclaimed, “O my God! how sweet it is to die in Thine arms!”
On the 13th of December 1803, at the age of seventy-two, Father Grou died at Lulworth Castle, where the Weld family had so nobly and generously offered him hospitality—a hospitality which he richly repaid by his excellent counsels, and by writing for Mr. Weld and his children some of his most valuable ascetic works.
His manuscripts, which were numerous, were given up to his former companions, who in 1815 published L’Intérieur de Jesus et de Marie (The Inner Life of Jesus and Mary), an esteemed work which has been reprinted several times since.
- Characteristics of true devotion
- The Christian Sanctified by the Lord's Prayer
- The Hidden Life of the Soul
- How to Pray
- The Interior of Jesus and Mary
- The Ladder of Sanctity
- A Little Book on the Love of God
- Manual for Interior Soul
- Meditations on the Love of God
- The Practical Science of the Cross
- The Spiritual Maxims of Père Grou
- "Grou, Jean Nicolas", New Catholic Encyclopedia.
- Yancey, Philip. Prayer. Grand Rapids: Zondervan, 2006. Page 296.
- "A Short Sketch of the Author and His Works", in Grou, The Characteristics of True Devotion (New York: Benzinger Brothers, 1895) p. 15.
- "A Short Account of the Abbé Grou" (extracted from a longer notice which appeared in L'Ami de la Religion, Vol xxxiii., p. 65 et seq.) in Grou, Manual for Interior Souls (London: S. Anselm's Society, 1890), pp.xi–xii.
- "Short Sketch", pp. 15–16.
- "Short Account", p. xii.
- "Short Sketch", p. 16.
- "Short Account", pp. xii–xiii.
- "Short Account", pp. xiii–xiv.
- "Short Account", pp. xiv–xv.
- "Short Account", p. xv.
- "Short Account", pp. xv–xvi.
- "Short Account", p. xvi.
- "Short Sketch", p. 17.
- Characteristics of true devotion, by the author of 'The hidden life of the ... - Jean Nicolas Grou - Google Boeken. Books.google.com. Retrieved 2012-11-11.
- The Christian Sanctified by the Lord's Prayer - Jean Nicolas Grou - Google Boeken. Books.google.com. Retrieved 2012-11-11.
- The hidden life of the soul - Jean Nicolas Grou - Google Boeken. Books.google.com. Retrieved 2012-11-11.
- How To Pray - Jean Nicolas Grou, Joseph Dalby - Google Boeken. Books.google.com. Retrieved 2012-11-11.
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- Manual for Interior Souls: A Collection of Unpublished Writings - Jean Nicolas Grou - Google Boeken. Books.google.com. Retrieved 2012-11-11.
- "Manual for interior souls : a collection of unpublished writings : Grou, Jean Nicolas, 1731-1803 : Free Download & Streaming : Internet Archive". Archive.org. Retrieved 2012-11-11.
- Meditations on the love of God, in the form of a retreat and an instruction ... - Jean Nicolas Grou - Google Boeken. Books.google.com. Retrieved 2012-11-11.
- The practical science of the Cross in the use of the sacraments of penance ... - Jean Nicolas Grou - Google Boeken. Books.google.com. Retrieved 2012-11-11.
- The spiritual maxims of pčre Grou - Jean Nicolas Grou - Google Boeken. Books.google.com. Retrieved 2012-11-11.
- "Loyd Avery". Open Library. Retrieved 2012-11-11.
- "Jean-Nicholas Grou". LibraryThing. Retrieved 2012-11-11.