After passing through thirty-three and a half years of human living, Christ was cut off (Dan. 9:26). That means He was crucified.
After being cut off, crucified, Christ was resurrected to be begotten as the firstborn Son of God (Psa. 2:7; Acts 13:33; Heb. 1:5-6). Psalm 2 shows us Christ's resurrection. The word resurrection is not there, but the fact is there. Verse 7 says, "I will recount the decree of Jehovah;/He said to Me: You are My Son;/Today I have begotten You." "Today" is the day of Christ's resurrection. In Acts 13:33 Paul quoted Psalm 2:7, telling us that this refers to Christ's resurrection. In His resurrection, Christ was begotten. Since He was already the Son of God, why did He need to be begotten as the Son of God in resurrection? Christ was the only begotten Son of God in His divinity (John 3:16), but when He became incarnated, He put humanity upon Him. This humanity had nothing to do with the sonship of God, but through His death and resurrection, His humanity was "sonized" to also be the Son of God. By resurrection Christ brought His humanity into the divine sonship and was designated the Son of God with His humanity (Rom. 1:4). Now the Son of God has the divine nature with the human nature. When Christ was merely the only begotten Son of God, He was God's Son only in the divine nature. Now as the firstborn Son of God, He possesses both the divine nature and the human nature.
Christ is the firstborn Son of God, and we are the many sons of God. We believers in Christ are regenerated sons of God, having God's life and God's nature, but we also have our human nature. Our human nature is still in the process of being begotten. We have been regenerated in our spirit, but we still have not been transfigured in our body. When our body is transfigured, redeemed, glorified, our body will also be "sonized." Our sonship will be completed by that time (Rom. 8:23). The sonship began with the regeneration of our spirit, is continuing with the transformation of our soul, and will be consummated with the redemption of our body. The process of our sonship passes through our regeneration and transformation to our glorification.
In Psalm 2 we can see God's economy with God's kingdom and the resurrection of Christ, in which He was begotten to be God's firstborn Son. The day of resurrection was a great day. Not only was Christ born on that day, but we also were born on that day. First Peter 1:3 says that through Christ's resurrection, God regenerated us. When Christ was born as the firstborn Son of God, we were all born with Him to be His many brothers, the many sons of God (Rom. 8:29). Christ's resurrection was a big delivery, a big birth, of Himself as the firstborn Son of God with His many brothers, the many sons of God.