One of the most striking disagreements in the early church and even today was on the question of the virginity of Mary at Christ's birth and thereafter.
In the early church and even still today, we all agree that a virgin conceived and carried to term Christ. The disagreement was on what happened next at His birth. This disagreement subsequently also factored into the question of the relationship of the brothers of Jesus; were they also born from Mary or from elsewhere? We won't go into that issue, but will focus on the birth of Christ. There are two diametrically opposed views.
Which Gate and How?
To understand the conflict in the very early church, we will start with John of Damacus who wrote something remarkable around 725.
But just as He who was conceived kept her who conceived still virgin, in like manner also He who was born preserved her virginity intact, only passing through her and keeping her closed. The conception, indeed, was through the sense of hearing, but the birth through the usual path by which children come, although some tell tales of His birth through the side of the Mother of God. For it was not impossible for Him to have come by this gate, without injuring her seal in anyway.
John tells us of the belief in a "normal" birth through the "south gate". Apparently he believes that, but has no way to explain it. He also references the belief Christ was born out the "east gate"; that is, from Mary's side. He even gives credence to this belief as "not impossible". [added editions are in brackets] [OTOH, John may be referencing again the "south gate"; that it wasn't impossible to remain intact (somehow).] So to where does this idea arise [of a "normal" birth but with gate(s) regardless of south or east remaining intact]?
The idea sources to the infancy gospel of James wherein it is said that Mary remained a virgin even in the act of giving birth. This means one of two things. Neither are good. One she retained all of the afterbirth (placenta, blood, umbilical cord, etc). Two she was never really pregnant with Christ. This group was lead by Origen, Valentinus, and others.
As mentioned, this idea stays alive all the way to John of Damascus still commenting on the idea that Christ was born from Mary's side (east gate). Moreover we find the idea in the Trullo Council 692 in Constantinople defining no afterbirth at Christ's birth in Canon LXXIX.
As the Catholic Church has always taught the Virgin-birth as well as the Virgin-conception of our Blessed Lord, and has affirmed that Mary was ever-virgin, even after she had brought forth the incarnate Son, so it follows necessarily that there could be no childbed nor puerperal flux.
No childbed or birth flux, which means no afterbirth, umbilical cord, blood, placenta or all the normal things from a normal human birth. That was what was denied according to this view.
Here again is the source of this idea.
And the midwife went forth out of the cave, and Salome met her. And she said to her: Salome, Salome, I have a strange sight to relate to thee: a virgin has brought forth -- a thing which her nature admits not of.
Why? Her nature of being pregnant would be to bring forth a newborn, but also the rest of what it means to be pregnant.
Valentinus put it this way.
“he has brought his body down from above and passed through the Virgin Mary like water through a pipe. He has taken nothing from the virgin womb…”
Panarion of Epiphanius H7
Marcion, quoted from Tertullian, put it this way, denying the afterbirth, the normal birth in the normal human way.
Of course you [Marcion] are horrified also at the infant, which is shed into life with the embarrassments which accompany it from the womb;6991 you likewise, of course, loathe it even after it is washed, when it is dressed out in its swaddling-clothes, graced with repeated anointing, smiled on with nurse’s fawns. This reverend course of nature, you, O Marcion, (are pleased to) spit upon; and yet, in what way were you born? You detest a human being at his birth; then after what fashion do you love anybody? Yourself, of course, you had no love of, when you departed from the Church and the faith of Christ.
Ouch. Tertullian draws a line in the sand here between believing as the Church does in a normal human birth versus the "not normal". Unfortunately again, this idea nonetheless remained within and found its way some 550 years later in the aforementioned Council Canon.
Normal Birth in the Normal Way
On the other hand you have those in the church who agreed that Christ was born normally in the normal way. This meant exactly what it means (virginity, defined as intactness, was ended). This group was lead by Tertullian, Clement of Alexandria, Cyril of Jerusalem, and others.
I've already shown Tertullian commenting on the false idea of ever-virgin due to the idea of Mary retaining the after-birth or not even having any. Here is Clement of Alexandria who wrote about 200 also coming against that idea. He also mentions the source (Infancy Gospel of James).
"But, as appears, many even down to our own time regard Mary, on account of the birth of her child, as having been in the puerperal state, although she was not. For some say that, after she brought forth, she was found, when examined, to be a virgin."
That is to say they taught that Mary because of Jesus' birth remained in the childbirth state, remained a virgin after she brought forth, but Clement disagrees with them.
The context of Clement's quote is found in the first sentence and provides more clarity.
But those who are ready to toil in the most excellent pursuits, will not desist from the search after truth, till they get the demonstration from the Scriptures themselves.
Again his conclusion is not that Mary remained in the birth state as a perpetual virgin, but rather that scripture remained virginal.
Now [in contrast to the heretics] such to us are the Scriptures of the Lord, which gave birth to the truth and continue virgin, in the concealment of the mysteries of the truth.
Cyril of Jerusalem wrote about 350 and lays out the same argument that the only way Christ took flesh was to be born normally of the virgin. Note his insistence against the heretics on when that ended because Christ was both Son of God and Son of Man.
- Since God then beareth witness, and the Holy Ghost joins in the witness, and Christ says, Why do ye seek to kill me, a man who has told you the truth let the heretics be silenced who speak against His humanity, for they speak against Him, who saith, Handle me, and see; for a spirit hath not flesh and bones, as ye see me have. Adored be the Lord the Virgin-born, and let Virgins acknowledge the crown of their own state: let the order also of Solitaries acknowledge the glory of chastity for we men are not deprived of the dignity of chastity. In the Virgin’s womb the Saviour’s period of nine months was passed: but the Lord was for thirty and three years a man: so that if a virgin glories because of the nine months, much more we because of the many years.
Let me men glory because of Christ's virginity. Let the women glory for the Virgin Mary's 9 months. 9 months, not her whole life because to do so was to support the heretical idea that Christ took nothing from the Virgin and merely passed through her.
It may seem strange to our ears to hear this conflict in the words of those from some 2,000 years ago as they argued about the nature of Christ. After all, most Christians would agree He is Son of God and Son of Man; they just aren't sure how. Still that was the context of the argument about the nature of His birth and thus His nature. Did He just pass through Mary or was He born normally? Was there just an appearing or was the birth human complete with umbilical cord, blood, and placenta?
On the one side were those like Valentinus, Marcion, and Origen who believed and taught that Jesus took nothing from Mary and merely passed through her. They taught there was no normal birth, but rather that Christ just apppeared at her side. She remained in the childbirth state as a virgin.
On the other side were men like Tertullian, Clement of Alexandria, and Cyril of Alexandria who taught that Christ was born normally. Let the virgins glory in Mary's nine months.