firstborn: the eldest child and heir, and by extension the one who holds the firstborn's rank of first place, inheritance, and family headship
In its plainest use the word names the child born first. Under Israel's law that son inherited a double share, led the household after his father, and was set apart for God, so the word always carried more than a bare fact of birth order.
Long before the New Testament, Greek-speaking Jews had already stretched the word past birth order altogether. Their Scriptures call:
- Israel God's firstborn though it was not the first nation
- Ephraim firstborn though he was the younger brother
- David firstborn though he was the youngest of Jesse's sons, naming him the highest of the kings of the earth
In those places firstborn is a rank of supreme heir, something conferred, not a claim about who was born first.
The New Testament inherits that whole range and applies it to Jesus. When it calls him firstborn of all creation, firstborn from the dead, and firstborn among many brothers, the weight falls on his standing as heir and head, not on when he came into being. Where his resurrection is in view, the older note of being first in time returns and stands alongside the note of rank.
The senses hold together because in Israel the firstborn son was at once first in time and first in standing. The word can lean on either pole as the context requires, and often carries both at once.