“The miraculous effect of the life-giving Cross upon our souls, tortured by the poison of evil, proves to us most undoubtedly and clearly: (1) That we have indeed a soul, a spiritual being; (2) That there are evil spirits, harming our souls; (3) That God exists and our Lord Jesus Christ, and that He is always with us through His Divinity; and (4) That He has indeed accomplished our salvation by His sufferings and death on the Cross, and has destroyed the power of the Devil by means of the Cross..”
(St John of Kronstadt,  ‘My Life in Christ’)