In the beginning of the ages, when there was no time, God is/was/will be. He simply is – He exists by Himself, through Himself, and no one is needed for Him to just be. Here, Christ was the Only Begotten Son of God, being part of the Divine Trinity. But God’s desire, His intention, was to have many sons who are just like Christ. He wanted a mass-reproduction of Christ in humanity. This is when TIME came into being, and in time God Himself became a man in the person of the Lord Jesus Christ. As a man, on the earth, the Lord Jesus was God’s Only Begotten Son(Matt. 3:16), and He lived a perfect life on the earth, fully expressing God in His human living. Christ’s incarnation was the first step taken by God to accomplish His desire.
Through His resurrection, according to Rom. 1:3-4, Christ as the Only Begotten Son of God was designated Son of God in power – He was begotten to be the Firstborn Son of God! He was the Son of God in His divinity, but now He was begotten as the Firstborn Son of God in His humanity – as a Man, Christ is the Firstborn Son of God! Now as the Firstborn Son of God He is leading many sons into glory(Heb. 2:10), and all the other sons are being conformed to His image(Rom. 8:29)!
The way God accomplishes His intention is not like we achieve a mass reproduction(that is, by making a prototype and then mass-produce the rest according to the prototype) – God produced Christ as the Prototype, and now He is working Christ into His believers! We are men, with the human nature, but at one point God came into us and started the process of “son-izing” of our whole being. God in Christ as the Spirit came into our spirit and regenerated it – now throughout our Christian life, every day, and even more when we turn to Him to contact Him in our spirit, God is sonizing our humanity. He is making us His Sons in full in all our human being, in our entire tripartite being. Our human virtues are being uplifted, our fallen self is being denied, our fleshly members are being put to death – the enemy in us is being defeated, and the divine life swallows us up – growing in us, maturing us, developing in us, until we become not just Children of God(Rom. 8:16) but also Sons of God(Rom. 8:14) and even heirs of God(Rom. 8:17). Eventually, we are the many sons of God expressing Him in full, identical with His FirstBorn Son, Jesus Christ! And all this is accomplished by the divine life in us!