[cont.]
“This is my first born son, the first born of his mother”.
The Greek for “firstborn” (“prōtotokos”) can, and often does, simply means “preeminent” (Colossians 1:15,18), as well as simply meaning “firstborn, but not necessarily ‘first among others.’” However, it can, and does, mean “first among others” (Hebrews 11:28). This passage refers back to the OT when all the “firstborn” in Egypt were killed by the “angel of death” if the blood of the doorposts & lintels weren’t smeared with blood. Obviously, not
all of these households had only children who perished. At least some of them had other children, and only the “firstborn” perished.
When the NT writers wished to convey someone was an only child, they would use “only begotten” (“monogenēs”), such as Jesus being the “only begotten” (“monogenēs”) Son of God the Father (John 3:16), meaning Jesus did not have other heavenly “God-brothers,” rather than “firstborn” (“prōtotokos”).
“Monogenēs” simply means “single of its kind, only,” while when “prōtotokos” is used it more specifically refers to a child who has other siblings (Hebrews 11:28). This is why Protestants & others believe when Jesus is referred to as
Mary’s “firstborn Son” (Matthew 1:25; Luke 2:7), the NT writers specifically used “prōtotokos,” instead of “monogenēs.” The understanding is if they wished to convey Jesus was an only Child, even after He was born & grew up, they would have utilized “monogenēs,” instead.
At least that is the Protestant argument exegeting from the Greek.