Tradition
St. Cyril of Jerusalem
Catechetical Lectures
Book 23 › Section 13
13. Your kingdom come. A pure soul can say with boldness, Your kingdom come; for he who has heard Paul saying, Let not therefore sin reign in your mortal body, and has cleansed himself in deed, and thought, and word, will say to God, Your kingdom come.
Source: Catechetical Lectures (New Advent)