In NME culture, the firstborn, especially the firstborn son, was very special indeed. He had privileges and perquisites subsequent children did not. Interestingly, one of the titles for Jesus is
"Firstborn of all creation" (Colossians 1:15).
This expression does not mean Jesus was created; it does mean that He bears the honorific title of Firstborn, with all the privileges that accrue from being so named. Moreover, He is the creator of all things (ibid., v.16); He existed before all things and holds all things together by the word of His power (ibid., v.17); He is the head of the church, His body; He is the beginning, the firstborn from the dead; He has the first place in everything (ibid., v.18); and all the fullness of Deity dwells in Him (ibid., v.19).
Perhaps the greatest verse to indicate the equality of Jesus with the Father (besides Jesus' own words, "He who has seen me has seen the Father. The Father and I are one person," John 10:30; 14:19; 17:21) is Colossians 2:9,
"For in [Jesus] all the fullness of Deity dwells in bodily form."
This verse does not say that Jesus became Divine when He came to earth as a baby, born of the virgin Mary. He was God the Son in eternity, and He never ceased being God the Son, even during the 33 years of His self-emptying life on earth as the God-Man, Jesus Christ (see Philippians 2:7 ff.). Moreover, He will never cease being God, albeit as God in the flesh-and-bone body of a man.
Within the triune Godhead, there is one shining star, and that is Jesus Christ, the only begotten Son of God. No one preceded Him; no one followed Him. He is sui generis, as the French say. While some Roman Catholics will disagree with me on this point, the eternal Son of God, the second person of the trinity, was neither conceived nor born; He simply is:
"Jesus Christ, the same yesterday, today, and forever (Hebrews 13:8)."
In eternity past, the Son was the delight of His Father, and the Father of the Son. In other words, they loved one another, and always will. Moreover, each person in the Trinity seems to have a unique, yet overlapping, role to play. Concerning the Father and the Son, Jesus said,
"'All things have been handed over [or delegated] to Me by My Father; and no one knows the Son except the Father; nor does anyone know the Father except the Son, and anyone to whom the Son wills to reveal Him'" (Mt 11:27; Lk 10:22).
While your question bypasses the role of the Holy Spirit, He too has been delegated a role; namely, to reveal Jesus to people by removing the blindness from their spiritual eyes and by imparting Jesus' words of life to them, first, when they are first born from above, and second, as they grow in Christ. Christ, in other words, is formed in us by the unseen work of the Holy Spirit of God during the lifelong process of sanctification.
The Trinity is indeed a mind-blowing doctrine, neither easily explained nor easily understood. It is, however, part of the bedrock of the Christian faith. The only acceptable sacrifice for sin had to be both fully God and fully man, the infinitely perfect, spotless, and holy Lamb of God. Anything less would not suffice to put away sin by the sacrifice of Himself (Heb 9:26).