In His resurrection Christ as the God-man, in His humanity, was begotten of God (Acts 13:33). Before His resurrection Christ was the Son of God already. Why then did He need to be begotten of God? The answer is that before His resurrection, Christ was the only begotten Son of God (John 1:18). Not only so, when He was the only begotten Son, He was only divine; He was not human. He had only divinity; He did not have humanity. He had only the divine nature without the human nature. Through incarnation He became a God-man. In the aspect of His being God, He no doubt was divine. But in the aspect of His being a man, He was not divine before His resurrection. In His resurrection He "sonized" His humanity. Before His resurrection He was the Son of God in His divinity, but He was not the Son of God in His humanity. However, Acts 13:33 tells us that Christ's resurrection was a birth. In His resurrection He was begotten of God to be the firstborn Son of God (Rom. 8:29b). Christ's resurrection was a great birth, a great delivery, of a corporate child, which includes Christ and all His believers (John 20:17). He as the Son of Man was born of God to be the firstborn Son of God. Now, as the firstborn Son of God, He is both divine and human. He possesses two natures: the divine nature and the human nature. Hebrews 1:6 says that when the Lord Jesus comes back, He will not come as the Only Begotten but as the firstborn Son of God. This also is the produce of Christ's resurrection. Christ's resurrection produced the firstborn Son of God.
Christ as the firstborn Son of God is a model for conforming many sons to His image (Rom. 8:29a). If He were not human, how could we, who are human, be conformed to His image? If He were not human, He would not have a human image. But today He is both divine and human. He is God in God's form, in God's image, and He is also man in man's form, in man's image. He is divine and human, and we are human and divine. Thus, we can be conformed to His image. He is the model; we are the mass production, the many sons of God. Hence, Christ's resurrection also produced many sons of God.
In His resurrection Christ as the resurrection life regenerated all His believers (1 Pet. 1:3). Christ's believers are His brothers, and His brothers are the many sons of God (Heb. 2:10a, 11b-12; Rom. 8:29b). In this way Christ has become our inner life. He is the firstborn Son of God, and He has made us the many sons of God.
The many sons of God are the members of God's household to be God's kingdom (Eph. 2:19; Gal. 6:10) and God's precious inheritance (Eph. 1:11). Before Christ's resurrection God had a home, but in that home there were no children. Before Christ's resurrection, God, in a sense, was childless. It was through Christ's resurrection that God begot the firstborn Son and the many sons. Thus, from that time God began to have a family, a household. Eventually, this household becomes God's kingdom, and the children of God, the household of God, become God's precious inheritance. As God's many sons, we are God's inheritance. God considers only us, His sons, as His inheritance.