Translated by Allan Menzies.
When and to whom the Learning derived from Philosophy may be of Service for the Exposition of the Holy Scriptures; with a lively Personal Appeal.
This letter to Gregory, afterwards bishop of Caesarea, and called Thaumaturgus, was preserved in the Philocalia, or collection of extracts from Origen's works drawn up by Gregory of Nyssa and Basil of Caesarea. It is printed by Delarue and Lommatzsch in the forefront of their editions of the works. It forms a good preface to the commentaries, as it shows how Origen considered the study of Scripture to be the highest of all studies, and how he regarded scientific learning, in which he was himself a master, as merely preparatory for this supreme learning. Draeseke  has shown that it was written about 235, when Origen, after having had Gregory as his pupil at Caesarea for some years, had fled before the persecution under Maximinus Thrax to Cappadocia; while Gregory, to judge from the tenor of this Epistle, had gone to Egypt. The Panegyric on Origen, pronounced by Gregory at Caesarea about 239, when the school had reassembled there after the persecution, shows that the master's solicitude for his pupil's true advancement was not disappointed.
 Jahrbucher fur Prot. Theol. 1881, 1.
Reference address : https://www.ellopos.net/elpenor/greek-texts/fathers/origen/letter-gregory.asp