"At every hour and moment let us guard the heart with all diligence from thoughts that obscure the soul's mirror; for in that mirror Jesus Christ, the wisdom and power of God the Father, is typified and luminously reflected. And let us unceasingly seek the kingdom of heaven inside our heart, the seed, the pearl, and the leaven. Indeed, if we cleanse the eye of the intellect we will find all things hidden within us. This is why our Lord Jesus Christ said that the kingdom of heaven is within us, indicating that the Divinity dwells in our hearts." 

- St Philotheos of Sinai (9th or 10th Century) -