St. John on the Jesus Prayer:
The remembrance of the name of Jesus rouses the enemy to battle. For a soul that forces itself to pray the Prayer of Jesus can find anything by this prayer, both good and evil. First it can see evil in the recesses of its own heart, and afterwards good. This prayer can stir the snake to action, and this prayer can lay it low. This prayer can expose the sin that is living in us, and this prayer can eradicate it. This prayer can stir up in the heart all the power of the enemy, and this prayer can conquer it and gradually root it out. The name of the Lord Jesus Christ, as it descends into the depths of the heart, will subdue the snake which controls its ranges, and will save and quicken the soul. Continue constantly in the name of the Lord Jesus that the heart may swallow the Lord and the Lord the heart, and that these two may be one. However, this is not accomplished in a single day, nor in two days, but requires many years and much time. Much time and labor are needed in order to expel the enemy and instate Christ. Letter to Monks (PG 60, p. 753).
This quote from the great preacher of Orthodoxy, echoes the thoughts of St. Macarius on the contents of the heart:
The heart itself is but a small vessel, yet dragons are there, and there are also lions; there are poisonous beasts and all the treasures of evil. But there too is God, the angels, the life and the kingdom, the light and the apostles, the heavenly cities and the treasuries of grace—all things are there. (H.43.7)
It also reinforces postings on this blog which speak of the “slowness of grace.” Thus we are not only enjoined to be vigilant, but also to be patient.