Today Christ is the Son of God in two respects: He is God's only begotten Son and He is also God's firstborn Son. However, if He were only God's only begotten Son, He could not have any brothers. To have us as His brothers, He must possess humanity; but as God's only begotten Son in eternity past, He possessed only divinity, not humanity. Nevertheless, in His incarnation Christ put on humanity, and through resurrection He brought this humanity into sonship. In this way He became God's firstborn Son with both divinity and humanity. Then, as the life-giving Spirit, He entered into us to make us also sons of God. Now we are the many sons of God being conformed to the image, not of God's only begotten Son, but of His firstborn Son. Therefore, as God's firstborn Son, Christ has many brothers. We all need to see that being born as the firstborn Son of God was a great work which Christ accomplished through His resurrection. Although it is clearly taught in the Bible, many Christians have never seen this matter.
On the day of His resurrection Christ was begotten by God in His humanity. He became the firstborn Son of God in order to produce many sons of God. We need to realize that the date of our regeneration was the date of Christ's resurrection. When Christ was resurrected from among the dead, we, all the believers, were resurrected with Him (1 Pet. 1:3). Through His resurrection He was born to be God's firstborn Son, and at the same time all His believers were born to be the many sons of God. On the day of Christ's resurrection, all God's chosen people were resurrected and were born to be God's many sons. Now God has many sons with both divinity and humanity. But among these many sons, only the Firstborn is His only begotten Son. This only begotten Son of God, in His resurrected humanity, is also the firstborn Son of God. As the firstborn Son of God, He has both divinity and humanity, and we His believers as God's many sons also possess both the human nature and the divine nature (2 Pet. 1:4). Now day by day we are being conformed to the image of God's firstborn Son (Rom. 8:29).
In His resurrection Christ also released His divine life for His propagation (John 12:24; 1 Pet. 1:3). When the Lord Jesus died as the grain of wheat, His inner divine life rose up to grow. In His resurrection this life was released to produce many grains as His multiplication. This multiplication is His propagation. The one grain was propagated into many grains. Christ accomplished this great work in His resurrection.