When thoughts invade you, in place of weapons call on the Lord Jesus frequently and persistently and then they will retreat; for they cannot bear the warmth produced in the heart by prayer and they flee as if scorched by fire. St John Klimakos tells us, ‘Lash your enemies with the name of Jesus’, because God is a fire the cauterizes wickedness (cf. Deut. 4:24; Heb.12:29). The Lord is prompt to help and will speedily come to the defence of those who wholeheartedly call on Him day and night (cf. Luke 18:7).
St. Gregory of Sinai