He is popularly known as the presumed author of the concept of Moscow as the Third Rome; Philotheus set out this thesis in his letters[1] to the priest Mikhail Grigorievich Misyur-Munekhin [ru] and to Grand Duke Vasily III.
Their main message in this regard is rather to remind the tzar about his ecclesiastical position of Protector of Faith, as the two previous capitals of Orthodoxy, Rome and Constantinople, both fell, first to the Latin heretics, and second to the Muslim heathens, with Moscow remaining its sole bastion.
Philotheus prophecy could then best construed that the Muscovy (or Russia in general) will stand as far as it remains true to the Orthodox faith.
His alleged authorship of the essays On the Grievances of the Church to Ivan the Terrible, was refuted by scholars, as it contained elements of discrepancy with his first epistle.
The person who wrote this essay, using the name of Philotheus, tied the theme of "Third Rome" to the protection of property rights of the church.