Hügel remained an Austrian citizen until he found himself to be a "hostile alien" after Britain declared war on Austria-Hungary in August 1914.

The scope of his learning was impressive, and the list of his correspondents reads like a "who's who" of nineteenth- and early twentieth-century European religious leadership (for example, Louis Duchesne, Alfred Loisy, Germain Morin, Maurice Blondel, Henri Brémond, John Henry Newman, William George Ward, Wilfrid Philip Ward, Lord Halifax, Cuthbert Butler, Claude Montefiore, George Tyrrell, Maude Petre, Evelyn Underhill, Antonio Fogazzaro, Ernesto Buonaiuti, Rudolf Christoph Eucken, Hans Vaihinger, Franz Xaver Kraus, and Ernst Troeltsch).

[14] Hügel did much to bring the work of the philosophers Eucken and Troeltsch to the attention of the English-speaking public, despite the hostility during and after the First World War to all things German.

Baron von Hügel was deeply engaged in theological discussions with a wide group of scholars associated with the turn-of-the-century Modernist controversy.

"He shared with other modernists a belief that science had raised new questions for religious faith and that undermined any naïve suppositions that believers could rely purely on dogmatic authority as a source of truth.

"[2] His scholarly concerns included the relationship of Christianity to history, ecumenism, mysticism, the philosophy of religion, and the rejection of much of the immanentism in nineteenth-century theology.

[16] Under Pope Pius X, prompted by conservatives such as Cardinal Merry del Val y Zulueta, there was a backlash against many of the Modernist thinkers, and Hügel attempted to negotiate a middle way of restraint, while remaining true to the principles of intellectual rigour and free enquiry.

Friedrich von Hügel's major work was The Mystical Element of Religion as Studied in St. Catherine of Genoa and Her Friends (1908).

Writing in The Manchester Guardian after Hügel's death, William Temple gave his judgement of its value: It is quite arguable that this is the most important theological work written in the English language during the last half-century.

The most striking section of it — the introduction — has so deeply permeated the thought of our time that its leading conception has become a commonplace among many who have never read the book, or even who have never heard of it.

His friend George Tyrrell observed, "All life, according to [Hügel] consists in a patient struggle with irreconcilables—a progressive unifying of parts that will never fit perfectly.

The body of Saint Teresa lies undecayed in tomb, Bathed in miraculous oil, sweet odours from it come, Healing from its lettered slab.