Can a first born be God?
I think many people have a hard time with the concept that the Son of God was born. It's just that if He was (and is) God, how could he be the Son of God, born of a woman?
Consider these two things...
First: Birth does not mean the beginning of life. It is not the start of existence. The manger was not the real beginning. It was A beginning, but not The beginning, if you know what I mean. For the many people who believe that life began at birth, they are simply wrong. They have either never been pregnant, or they have not ever had the opportunity to know a pregnant woman.
All things were made through Him, and without Him nothing was made that was made. - John 1:3
So, the Savior did not make His first appearance in a feeding trough. We know that He created all things. That's pretty God-like.
Okay, so maybe you've thought of that, but there is another aspect to the idea of "firstborn" that we need to consider in regards to the Savior of all mankind. For that, we can look at the Torah.
Then the Lord spoke to Moses, saying: “Now behold, I Myself have taken the Levites from among the children of Israel instead of every firstborn who opens the womb among the children of Israel. Therefore the Levites shall be Mine, because all the firstborn are Mine. - Numbers 3:11-13
The second consideration here is that Jesus/Yeshua is our High Priest. While every couple had a first born child, Yahweh set apart the priests (Levites) as first born as well. They were dedicated as Yah's first born.
So Yeshua, the first born of Miriam was also set apart (consecrated as Holy) as a priest - our High Priest. So, even if he came to us the way He did throughout the Bible as Yah's right hand, as a messenger (as He did to Adam and Eve, Abraham, Joshua, etc.), He would still be the One who is the first born of all creation.
He is the image of the invisible God, the firstborn over all creation. Col. 1:15