Matthew 13:55
Matthew 13:5555“Isn’t this the carpenter’s son? Isn’t His mother’s name Mary, and aren’t His brothers James, Joseph, Simon, and Judas?
is a primary JW text against Catholic perpetual virginity of Mary. The verse names Jesus's brothers — James, Joseph, Simon, and Judas — and v. 56 mentions his sisters. The Watchtower reads adelphoi straightforwardly as biological half-brothers, Mary's other children, conceived after the virgin birth. The verse is treated as decisive evidence against perpetual virginity and as a wedge against Catholic Mariology more broadly.
Common ground with the Witness against Rome. Protestants read the same way: those are Jesus's biological half-brothers and half-sisters, Mary's other children. Jerome invented the "cousins" theory in AD 383 in his Against Helvidius specifically to preserve perpetual virginity, and the New Catholic Encyclopedia admits this. The Greek adelphoi in the Septuagint and New Testament regularly means biological brothers when used in family contexts; the cousins theory is imposed on the text to protect a doctrine that emerged centuries after the apostles. On Mary's other children, the Watchtower and the Protestant tradition agree against Rome. The pivot is to use the agreement to open the question of who her firstborn was — pair with (Immanuel = "with us is God") and ("in him all the fullness of the divine quality dwells bodily") to move from Mariology, where common ground exists, to Christology, where the real disagreement lies.