Matthew 1:25
From Textus Receptus
Matthew 1:25 And knew her not till she had brought forth her firstborn son: and he called his name JESUS.
Modern Versions also bring confusion about mary being a Virgin:
If it is only 'a son' rather than a 'firstborn son' Mary may have had other children before Jesus to someone else. So the Textus Receptus solves two errors by stating the fact that Jesus was May's firstborn:... See More
1) a firstborn implys that there was a secondborn later on (otherwise it would say 'only begotten')
2) A firstborn implys that Mary had previously had no other children.
Firstborn makes it impossible for these to heretical doctrines to survive.
See Also Psalm 69:8, Matthew 12:46; 13:55; Mark 3:31, 6:3; John 2:12; 7:3,5; 1 Corinthians 9:5, Galatians 1:19.
The Greek - πρωτότοκον (firstborn) appears in the vast majority of Manuscripts exept for 2 Papyrus (B and Aleph) and 3 miniscule mss.