He is also head of the body, the church; and He is the beginning, the firstborn from the dead, so that He Himself will come to have first place in everything. - Col 1:18
What is the importance of being "firstborn"? M-W provides this insight:
In many civilizations, past and present, the state of being the oldest among siblings is a key component of inheritance law. “Primogeniture,” which first appeared in English in the early 17th century, derives from the Late Latin “primogenitura,” a combination of the Latin “primus” (“first”) and “genitura” (“birth”), from the past participle of “gignere” (“to beget”). For those who are youngest in birth order, a similar word applies — “ultimogeniture” — but this word is newer (first appearing in English in 1882) and much less common.
The Torah also commands that we honor the firstborn:
If a man has two wives, the one loved and the other unloved, and both the loved and the unloved have borne him sons, if the firstborn son belongs to the unloved, then it shall be in the day he wills what he has to his sons, he cannot make the son of the loved the firstborn before the son of the unloved, who is the firstborn. But he shall acknowledge the firstborn, the son of the unloved, by giving him a double portion of all that he has, for he is the beginning of his strength; to him belongs the right of the firstborn. - Deut 21:15-17