How could God make dead men alive, so that God and man could again enjoy fellowship for all eternity? There was only one way. He had to give Himself to be man's life. He could not give out little portions of His life to save us, because God cannot be separated from His life any more than you can separate your own life from your body. Life is expressed in a body, and when the life departs, a man is dead. God's life is similar, but of a higher order. The only way we can partake of the life of God is to be united with God. This is why God gave Adam physical life, but could not give him spiritual life (His own life) in the same way. He could raise Lazarus from the physical grave by a command, but He could not raise him from spiritual death in the same way. Although we may never have considered these things in quite this way before, I believe it can help us to understand why Calvary is the foundation of God's plan.
How then could God become united with Adam? (We use "Adam" as the figurative name for the whole human race.) We were dead in sin, so the only way God could be united with Adam was to first be united with his condition of death. Then, by that union, He could raise Adam from the dead through the life God has in Himself. This is exactly what Jesus did! Jesus is God, and He first united with Adam's race by being born into a human body. He became as we are in every aspect except sin. "Inasmuch then as the children have partaken of flesh and blood, He Himself likewise shared in the same, that through death He might destroy him who had the power of death, that is, the devil, and release those who through fear of death were all their lifetime subject to bondage. For indeed He does not give aid to angels, but He does give aid to the seed of Abraham. Therefore, in all things He had to be made like His brethren, that He might be a merciful and faithful High Priest in things pertaining to God, to make propitiation for the sins of the people. For in that He Himself has suffered, being tempted, He is able to aid those who are tempted" (Hebrews 2:14-18).
Jesus, as the eternal Son of God, took on a human body and permanently identified with mankind, thus becoming the Son of Man. As Son of Man, He became like his brethren in all things, except that He was perfect and never sinned--and in reality He could not sin because He was God. Because His Father was God, He was not born in death as we are. He was the unique God-Man. He maintained a perfect relationship with His Father from the beginning to the very end of His life on earth. He was the perfect Lamb of God. He was perfected as our Savior, but not out of weakness and sin as we are. His "tempting" or testing was necessary, but only to reveal who He was. The devil thought he could cause Him to fall, but the devil himself was deceived to think that. "Though He was a Son, yet He learned obedience by the things which He suffered. And having been perfected, He became the author of eternal salvation to all who obey Him..." (Hebrews 5:8-9).
If Jesus was not born in sin and could not sin, how then could He be our Savior? How could He really understand our plight or meet our need? Until He underwent death at Calvary, He was not yet fully identified (united) with Adam, so He could not yet lift us out of death. It was at Calvary that His identification or union with mankind was completed. "For He made Him who knew no sin to be sin for us, that we might become the righteousness of God in Him" (2 Corinthians 5:21). "Now from the sixth hour until the ninth hour there was darkness over all the land. And about the ninth hour Jesus cried out with a loud voice, saying, 'Eli, Eli, lama sabachthani?' that is, 'My God, My God, why have You forsaken Me?'" (Matthew 27:45-46). In the final hour of the cross, Jesus became sin for us and suffered the result of sin, which is death. His identification with Adam was now complete, as He took the whole of Adam's sin upon Himself. In that hour of total abandonment to the will of God, Jesus entrusted Himself into the hands of His Father, who was able to raise Him out of the grave. "And when Jesus had cried out with a loud voice, He said, 'Father, into Your hands I commit My spirit.' Having said this, He breathed His last" (Luke 23:46).
Three days later, God raised Jesus triumphantly from the grave. "Him, being delivered by the determined purpose and foreknowledge of God, you have taken by lawless hands, have crucified, and put to death; whom God raised up, having loosed the pains of death, because it was not possible that He should be held by it" (Acts 2:23-24). When Jesus rose, He arose alone, but He would not be alone for long. In a few days a new family would begin to grow. Jesus arose as the Head of the new man, the "new Adam"--the Head of a new creation. God was beginning again in Christ, and this race would not fail, because it was based on God, His life, and His ability working within man.
After Jesus rose from the dead, He ascended to the Father and received the promise from the Father. "This Jesus God has raised up, of which we are all witnesses. Therefore being exalted to the right hand of God, and having received from the Father the promise of the Holy Spirit, He poured out this which you now see and hear" (Acts 2:32-33). On the day these words were spoken, the first group of 120 were raised up together with Christ in newness of life. They were baptized (filled) with the Holy Spirit (who is God) by Christ, and were thus united with Him in His resurrection. They were born of the Spirit into a new life in union with God. Old things passed away; now all things were new. What that first group of believers experienced is what every believer experiences when he comes to Jesus as Savior and Lord to receive life from above. Jesus takes us out of our death (separation from God) and brings us into His life (union with God). This is the glorious salvation that Jesus purchased for us at Calvary.