You do not know what firstborn means. It is about status.
Let me help you.
King David was the youngest of ten children, but he was the anointed King of Israel. He was God's firstborn and pre-eminent over all.
Manasseh was born first, but Ephraim is the "firstborn," not because he was born first, he wasn't, BUT Ephraim was pre-eminent over Manasseh, making him the firstborn.
When we are told Jesus is the firstborn over all creation, we are being told that Jesus is pre-eminent over all creation i.e. Jesus is Creator God, which is a re-affirmation of Col 1:16.
He (Jesus) is the image of the invisible God, the firstborn of all creation. For by him all things were created, in heaven and on earth, visible and invisible, whether thrones or dominions or rulers or authorities—all things were created through him and for him. And he is before (firstborn) all things, and in him all things hold together. And he is the head of the body, the church. He is the beginning, the firstborn from the dead, that in everything he might be pre-eminent. For in him all the fullness of God was pleased to dwell,
(Colossians 1:15-19 ESV)
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Firstborn, as in Christ was born taking on flesh and blood to become the First Born Son of God, and we are part of His family, and He our head.
It is also about Paul teaching Christ as the second Adam to be our Savior, the second Man is the Lord from heaven.
This was quite a wonderful thing He did for us, to make us part of His family in such an intimate way, to identify with us so completely.
He bore our image, and now, because of what He did for us, we will bear His image.
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1 Corinthians 15
45 And so it is written, “The first man Adam became a living being.” The last Adam became a life-giving spirit.
46 However, the spiritual is not first, but the natural, and afterward the spiritual. 47 The first man was of the earth, made of dust; the second Man is the Lord from heaven. 48 As was the man of dust, so also are those who are made of dust; and as is the heavenly Man, so also are those who are heavenly. 49 And as we have borne the image of the man of dust, we shall also bear the image of the heavenly Man.
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Romans 8:29 For whom he did foreknow, he also did predestinate to be conformed to the image of his Son, that he might be the firstborn among many brethren.
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Hebrews 12:23 To the general assembly and church of the firstborn, which are written in heaven, and to God the Judge of all, and to the spirits of just men made perfect,
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Hebrews 2
10 For it was fitting for Him, for whom are all things and by whom are all things, in bringing many sons to glory, to make the captain of their salvation perfect through sufferings. 11 For both He who sanctifies and those who are being sanctified are all of one, for which reason He is not ashamed to call them brethren, 12 saying:
“I will declare Your name to My brethren;
In the midst of the assembly I will sing praise to You.”
13 And again:
“I will put My trust in Him.”
And again:
“Here am I and the children whom God has given Me.”
14 Inasmuch then as the children have partaken of flesh and blood, He Himself likewise shared in the same, that through death He might destroy him who had the power of death, that is, the devil, 15 and release those who through fear of death were all their lifetime subject to bondage. 16 For indeed He does not give aid to angels, but He does give aid to the seed of Abraham. 17 Therefore, in all things He had to be made like His brethren, that He might be a merciful and faithful High Priest in things pertaining to God, to make propitiation for the sins of the people. 18 For in that He Himself has suffered, being tempted, He is able to aid those who are tempted.