This question concerns one of the most awe-inspiring facts about Christ impossible for the human mind to fully comprehend. But don’t be discouraged. If God were no bigger than our understanding, there is no way He could be God.
Rather than look at the “how,” though, let’s look at why this belief is essential to the Christian faith.
First off, the New Testament declares Jesus to be God. People just like you and me attested to His deity. His disciple Thomas, upon seeing Christ after His resurrection, exclaimed, “My Lord and my God” (John 20:28).
At the same time, we know from Scripture that Christ walked upon the earth completely human and “who, being in the form of God, did not consider it robbery to be equal with God, but made Himself of no reputation, taking the form of a bondservant, and coming in the likeness of men” (Phil. 2:6–7). It must be noted that in becoming man He did not give up His divine attributes, but instead was God in human flesh.
Why was that necessary? Christ must be fully God and fully man in order to rescue mankind.
As sinners, we face eternal separation from God in a place the Bible calls hell. Because God loves us, He does not want us to be separated from Him forever. Yet, a holy God must punish sin.
So, God devised a plan whereby somebody else could take our punishment for us. That somebody must be absolutely perfect. One sinner cannot die for another sinner. The only one who qualified was His fully divine Son Jesus Christ.
But to help us He had to become like us—human flesh and blood—and die on a cross as our substitute: “But God demonstrates His own love towards us, in that while we were yet sinners, Christ died for us” (Rom. 5:8). God punished His perfect Son where He should have punished us. The third day that Son arose victorious over sin and the grave.
Now all we need to do is receive what Jesus, the God-man did for us, by trusting Christ as our only way to heaven, our only way to a right relationship with God. The Bible so simply declares, “Most assuredly, I say to you, he who believes in Me has everlasting life” (John 6:47).
No other man has walked the earth as fully God and fully man. Overwhelmed, we should come to Him in brokenness and trust Him to save us.
What greater love could there be? Jesus Christ left heaven for earth and suffered the cruelest of all deaths on a cross—all so we could spend eternity with Him.