January 19th is the feast of St Macarius the Egyptian (eastern calendar).
When the rich men of the earth have brought much fruit into their garners, they set to work again every day to get more, in order to have plenty, and not run short.
If they presume upon the wealth laid up in the garners, and take things easily and add no more, but use up what they have stored already, they soon sink into want and poverty.
So they have to labour and add, enlarging their intake, that they may not get behindhand.
In Christianity, to taste of the grace of God is like that. Taste, it says, and see how gracious the Lord is (Psalm 35:8).
This tasting is an effectual power of the Spirit in full certainty, ministering in the heart.
As many as are the sons of light, and of the ministry of the New Covenant in the Holy Ghost, these have nothing to learn from men; they are taught of God (1 Thess. 4:9).
Grace itself writes upon their hearts the laws of the Spirit.
They ought not therefore to rest their assurance only upon the scriptures that are written in ink; the grace of God writes the laws of the Spirit and the mysteries of heaven upon the tables of the heart as well (2 Cor. 3:2).
For the heart governs and reigns over the whole bodily organism; and when grace possesses the ranges of the heart, it reigns over all the members and the thoughts.
For there, in the heart, is the mind, and all the faculties of the soul, and its expectation; therefore grace penetrates also to all the members of the body.
On the other hand, as many as are sons of darkness, sin reigns over their heart, and penetrates to all their members, for out of their hearts proceed evil thoughts (Matt. 15:19), and thus diffused puts the man in darkness.
Those who say that evil is not born and bred in man, may have no anxiety about tomorrow, nor any desire either.
For a certain length of time, evil ceases to cause trouble in them by suggesting some object of desire, so that a man will affirm on oath, “Such a passion no longer assails me.”
After a short while he is consumed with the desire, so that he is found guilty of perjury into the bargain.
As water runs through a pipe, so does sin through the heart and thoughts.
As many as will not have this notion, are refuted and mocked by sin itself, even if sin did not wish to triumph; for evil endeavours to escape notice and to be hidden in the mind of man.
Macarius the Egyptian (c. 300-391) [attributed]: Spiritual Homily 15, 20-21, trans. by A.J. Mason DD.