"the firstborn of all creation" (1:15). What does the letter say this means?

The letter doesn't explain it, and these notes don't either. Here are the letter's own words: "He is the image of the invisible God, the firstborn of all creation." (1:15) "For by him all things were created in the heavens and on the earth, visible things and invisible things, whether thrones or dominions or principalities or powers. All things have been created through him and for him." (1:16) "He is before all things, and in him all things are held together." (1:17) "He is the head of the body, the assembly, who is the beginning, the firstborn from the dead, that in all things he might have the preeminence." (1:18). The letter has the word firstborn twice, at 1:15 and 1:18. These are the letter's own words, as it gives them, and these notes add nothing to them and choose nothing.