A monk of Mount Athos who became archbishop of Thessalonica, he defended the prayer of the heart of the Hesychast monks against those who mocked it. He taught that God, unreachable in his essence, truly gives himself to be known through his light to those who are purified in silence.
In their own words
Lord, enlighten my darkness.
Habitual prayer (Life by Philotheos)
They shall be light and they shall see the light: a vision of joy and wholly holy, reserved for the purified heart alone.
Triads in Defence of the Holy Hesychasts, II, 3, 66 (translated from the Greek by the Manna team)