Topic 4
If any one affirms that Christ was born of the seed of man by the Virgin, in the same manner as all men are born, and refuses to acknowledge that He was made flesh by the Holy Spirit and the holy Virgin Mary, mad became man of the seed of David, even as it is written, let him be anathema.
Explication
How could one say that Christ was born of the seed of man by the Virgin, when the holy Gospel and the angel, in proclaiming the good tidings, testify of Mary the Virgin that she said, “How shall this be, seeing I know not a man?” Wherefore he says, “The Holy Ghost shall come upon you, and the power of the highest shall overshadow you: therefore also that holy thing which shall be born of you shall be called the Son of the Highest.” And to Joseph he says, “Fear not to take unto you Mary your wife: for that which is conceived in her is of the Holy Ghost. And she shall bring forth a son, and they shall call His name Jesus: for He shall save His people from their sins.”
Source: Twelve Topics on the Faith (New Advent)