Aside from John 2:12, the synoptic Gospels (Matthew, Luke and Mark) as well as some Epistles of St. Paul also mentions of Christ’s brothers and sisters. The Church always understood these passages as not referring to other children of the Virgin Mary. In fact James and Joseph “brothers of Jesus” are the sons of another Mary, a disciple of Christ, whom St. Matthew significantly calls “the” other Mary (Mt.13:55; 28:1, 27:56). They are close relations of Jesus Christ according to an Old Testament expression (Gen.13:8, 14:16. 29:15).Basing on this premise we conclude that the said “brothers” are not children of the Blessed Virgin Mary, but people who are closely associated to Christ either His cousins (held by most Church Fathers) or close followers.
Jesus Christ spoke in Aramaic an ancient Jewish language common in Judea, Nazareth and Galilee, where Jesus Christ spent most of His public ministry. Aramaic has a very limited vocabulary in fact the term “Brother” (Ahuy in Aramaic) is use to address blood-born brothers, cousins, relatives, countrymen, people belonging to a same community and racial group etc. The Hebrew language also shares the vocabulary limitation of Aramaic. The Old Testament was predominantly written in Hebrew (Except for Ezra, Jeremiah and Daniel which were written in Aramaic) in Genesis 13:8 Abram called lot his “brother” (Ach אָח in Hebrew) despite of Lot being his nephew.
Henceforth, during the time of Christ basing on the usage of the term “brother” in Aramaic everyone is calling each other as his brother as long as they belong to the same community, race, relatives etc.
To further our understanding of the term “brother” we have to also consider its usage in Koine Greek that language used to write the New Testament. Unlike Aramaic and Hebrew, Greek has a word used for close relatives (cousins, aunt, uncle) and that is “Suggenes”, and for blood-born brothers “adelphos”.
If the “brothers” mentioned in the Gospels are merely Christ’s close relatives why didn’t the New Testament writers use the term “suggenes” rather than “adelphos”? The New Testament writers are not only concerned in transmitting the message of Christ in the lingua franca of the people of their time which is Greek, but also preserve the continuity of Jewish culture from the Old Testament to the New Testament. Therefore, they have chosen to literally translate Aramaic words to Greek, i.e “ahuy” Aramaic for “brother” to “Adelphos” Greek for “brother” in order not to lose its meaning. In the Epistles of St. Paul the word “brother” was used 139 times in addressing fellow Christians. It would be beyond comprehension to conclude that St. Paul has 139 siblings. The term “brother” has the same usage in the Gospels.
The first one to assert that the “brothers” of the Lord stated in the Gospels are other children of the Blessed Virgin Mary is the heretic Helvidius. He was greatly rebuked by St. Jerome a master of the ancient languages of his time.
“But as regards to Victorinus, I assert what has already been proven from the gospel that he [Victorinus] spoke of the brethren of the Lord not as being sons of Mary but brethren in the sense I have explained, that is to say, brethren in point of kinship, not by mere nature.” [Against Helvidius: The Perpetual Virginity of Mary A.D 383]
Various Church Fathers from Ante-Nicene Fathers, Nicene-Fathers and Post-Nicene Fathers unanimously professed and believed that Mary has no other children, and remained a virgin before, during and after the birth of Jesus Christ.
The Reformers Luther, Calvin and Zwingli also shares the belief of the Church Fathers.
Helvidius displayed excessive ignorance in concluding that Mary must have had many sons, because Christ’s “brothers” are sometimes mentioned. [Harmony of Matthew, Mark & Luke, Sec. 39 (Geneva 1562), Vol.2, Calvin’s Commentaries]
Christ. . .was the only Son of Mary, and the Virgin Mary bore no children besides Him. . .I am inclined to agree with those who are declare that “brothers” really mean “cousins” here, for Holy Writ and the Jews always call cousins brothers. [Luther’s Works, Vol. 22, p.214/ Sermons on John, chapters 1-4.]
To deny that Mary remained ‘inviolata’ before, during and after the birth of her Son, was to doubt the omnipotence of God. . . [G. R. Potter, Zwingli/ The Perpetual Virginity of Mary (Sept. 17, 1522)]
In John 19:27 Jesus Christ entrusted His Mother Mary to His Disciple John. If Jesus Christ has other siblings it would be rude and against the Jewish custom to leave Mary to the care of John rather than His siblings. But the fact is Mary has no other children but Jesus Christ.