But as to how many days after her delivery a woman may enter the church, you have learned that by the direction of the Old Testament she ought to keep away 33 days for a male child, but 66 for a female. It should be known, however, that this is understood mystically. For, if in the same hour in which she has been delivered she enters the church, she subjects herself to no burden of sin. For it is the pleasure of the flesh, not the pain, that is in fault. But it is in the carnal intercourse that the pleasure lies; for in bringing forth of offspring there is pain and groaning. Whence even to the first mother of all it is said, In sorrow you shall bring forth children. If, therefore, we forbid a woman after her delivery to enter the church, we reckon her very penalty to her for a fault. Moreover, it is by no means forbidden that either a woman after delivery or that which she has brought forth should be baptized without delay, if in peril of death; she even in the same hour in which she is delivered, or it in the same hour in which it is born. For, as in the case of those who live and have discretion the grace of the holy mystery should be seen to with great discernment, so to those who are in imminent danger of death it should be offered without any delay, lest, while time is being sought for administering the mystery of redemption, death should shortly intervene, and no way be found of redeeming the time that has been lost.
Further, her husband ought not to cohabit with her till that which is brought forth be weaned. But an evil custom has arisen in the ways of married persons, that women scorn to nurse the children whom they bring forth, and deliver them to other women to be nursed. Which custom appears to have been devised for the sole cause of incontinency, in that, being unwilling to contain themselves, they think scorn to suckle their offspring. Those women therefore who, after an evil custom, deliver their children to others to be nursed ought not to have intercourse with their husbands unless the time of their purification has passed, seeing that, even without the reason of childbirth, they are forbidden to have intercourse with their husbands while held of their accustomed sicknesses; so much so that the sacred law smites with death any man who shall go into a woman having her sickness. Yet still a woman, while suffering from her accustomed sickness, ought not to be prohibited from entering the church, since the superfluity of nature cannot be imputed to her for guilt, and it is not just that she should be deprived of entrance into the church on account of what she suffers unwillingly. For we know that the woman who suffered from an issue of blood, coming humbly behind the Lord, touched the hem of his garment, and immediately her infirmity departed from her. If then one who had an issue of blood could laudably touch the Lord's garment, why should it be unlawful for one who suffers from a menstruum of blood to enter in the Lord's Church?
But that woman, you will say, was compelled by infirmity; but these are held of their accustomed sicknesses. Yet consider, dearest brother, how all that we suffer in this mortal flesh is of infirmity of nature, ordained after guilt by the fitting judgment of God. For to hunger and to thirst, to be hot, to be cold, to be weary, is of infirmity of nature. And to seek food against hunger, and drink against thirst, and cool air against heat, and clothing against cold, and rest against weariness, what is it but to search out certain healing appliances against sicknesses? For in females also the menstruous flow of their blood is a sickness. If therefore she presumed well who in her state of feebleness touched the Lord's garment, why should not what is granted to one person in infirmity be granted to all women who through defect of their nature are in infirmity?
Further, she ought not to be prohibited during these same days from receiving the mystery of holy communion. If, however, out of great reverence, she does not presume to receive, she is to be commended; but, if she should receive, she is not to be judged. For it is the part of good dispositions in some way to acknowledge their sins, even where there is no sin, since often without sin a thing is done which comes of sin. Whence also, when we hunger, we eat without sin, though it has come of the sin of the first man that we do hunger. For the menstruous habit in women is no sin, seeing that it occurs naturally; yet still that nature itself has been so vitiated as to be seen to be polluted even without the intention of the will is a defect that comes of sin, whereby human nature may perceive what through judgment it has come to be, so that man who voluntarily committed sin may bear the guilt of sin involuntarily. And so females, when they consider themselves as being in their habit of sickness, if they presume not to approach the sacrament of the body and blood of the Lord, are to be commended for their right consideration. But when, out of the habit of a religious life, they are seized with a love of the same mystery, they are not to be restrained, as we have said. For, as in the old Testament outward acts were attended to, so in the New Testament it is not so much what is done outwardly as what is thought inwardly that is regarded with close attention, that it may be punished with searching judgment. For while the law forbids the eating of many things as being unclean, the Lord nevertheless says in the Gospel, Not that which goes into the mouth defiles a man, but the things which come forth from the heart, these are they which defile a man. And soon after He added in explanation, Out of the heart proceed evil thoughts (Ib. 19). Hence it is abundantly indicated that what is shown by Almighty God to be polluted in act is that which is engendered of the root of polluted thought. Whence also Paul the Apostle says, All things are pure to the pure; but unto them that are defiled and unbelieving is nothing pure. And immediately, to declare the cause of this defilement, he subjoins, For their mind and conscience is defiled. If, then, food is not impure to one whose mind is not impure, why should what with a pure mind a woman suffers from nature be reckoned to her for impurity?
Further, a man after sleeping with his own wife ought not to enter the church unless washed with water, nor, even when washed, enter immediately. Now the law enjoined on the ancient people that a man after intercourse with a woman should both be washed with water and not enter the church before sunset. Which may be understood spiritually as meaning that a man has intercourse with a woman when his mind is joined with delight in thought to illicit concupiscence, and that, unless the fire of concupiscence in his mind should cool, he ought not to think himself worthy of the congregation of his brethren, seeing himself to be burdened with by lewdness of wrong desire. For, although in this matter different nations of men have different notions, and some are seen to observe one practice and some another, yet the usage of the Romans from ancient times has always been for a man after intercourse with his own wife both to seek the purification of the bath and to refrain reverently for a while from entering the church.
Source: Register of Letters (New Advent)