A reading from the works of St Cyril of Alexandria
He that eateth my Flesh and drinketh my Blood, saith the Lord, dwelleth in me, and I in him. If a man take two pieces of wax and melt them, and pour the one into the other, they necessarily mingle ; so also, he that receiveth the Body and Blood of the Lord doth become so joined with the Lord that he is to be found in Christ and Christ in him. Another comparison thou wilt find in Matthew. The Lord there saith : The kingdom of heaven is like unto leaven which a woman took, and hid in three measures of meal till whole was leavened. Even as Paul saith : A little leaven leaveneth the whole lump : so also doth a little of this Blessing draw the whole man unto itself, and fill him with its grace ; and thus doth Christ dwell in us, and we in Christ.
As for ourselves, if we would win life everlasting, if we would that the Giver of Immortality should dwell in us, let us run freely to receive this Blessing, and let us beware that the devil succeed not in laying a stumbling-block in our way, in the shape of a mistaken reverence. Thou rightly sayest, and we know well, how that it is written : Whosoever shall eat this Bread and drink this Cup of the Lord, unworthily, shall be guilty ; he eateth and drinketh judgment to himself. I therefore examine myself and find myself unworthy. And I ask thee, who citest these words to me, who is it that shall ever be found worthy? When, pray, wilt thou be such an one as may be worthy to be offered to Christ? For if, because of sin, thou art unworthy, and dost not cease to sin, (for as the Psalmist hath it : Who can tell how oft he offendeth?) then shalt thou on these grounds for ever lack this means of life and sanctification.
Wherefore I counsel thee to betake thee to godly thoughts, and to live as a zealous and devout servant of God, and then to make bold to receive this Blessing ; for it is a Blessing which, believe me, doth banish not death only, but all diseases likewise. For when Christ dwelleth in us, he stilleth the law of sin in our members, which warreth against the law of our mind. He giveth strength to godliness ; he turneth to calm the turbulent surging of our minds ; he cureth them which are sick ; he raiseth up them which are fallen ; and, as the Good Shepherd, which giveth his life for the sheep, he prevaileth that the sheep perish not.
From the Roman Breviary.