In the new movement of religious studies in Italy, he made the Holy Scriptures the centre of his intellectual activity; and, greatly assisted by his command of the Oriental languages—Greek, Hebrew, Arabic—by his experience of the Holy Places, by his knowledge of the major European languages, and by his relations with scholars of every country, he became an authority universally recognized and eagerly consulted in this field.
Within the modernist movement he exercised a moderating influence, and although denounced to Pius X as almost conniving with the rebels, he found in the Pope defence and protection; and he maintained a correspondence with him that bears witness to his faith, his evangelical uprightness, and his devotion to the Church. His learning was always in the service of apostolate, and this opened wide the field of his priestly ministry, first exercised at Ravenna, where he was very young as spiritual director and professor of Sacred Scripture in the Seminary; then for a longer period in Syria and Constantinople, where, by the wish of Leo XIII, he was attached to those Apostolic Delegations, devoting intense missionary activity there; and finally for thirty years in Rome. Missionary in the strictest sense of the word, Fr G. was for three years in the deadly regions of New Guinea, and after the First World War among the natives of the Putumayo, having been entrusted by Pius X with the task of reporting on the brutalities exercised by white masters against Indian negroes.
He concluded his missionary career with the apostolic visitation in the Ukraine, whither he had been sent by Benedict XV and later by Pius XI to report on a widespread movement for the union of the “Orthodox” with Rome, as it was taking shape in the territories of Russia restored to Poland by the war and in the regions bordering on Russia itself. Death prevented Benedict XV from creating him a cardinal.