First, why do we die? The Bible says: “Through one man [Adam] sin entered into the world and death through sin, and thus death spread to all men because they had all sinned.” (Romans 5:12)
Because God's Law to ancient Israel required "soul for soul [or, life for life]" (Exodus 21:23), the divine principle that could cover mankind's transgressions would have to equal what the first perfect man (Adam) had lost. Therefore, only the death of another perfect man could pay the wages of sin.
That perfect man was "Christ Jesus, who gave himself a corresponding ransom for all." (1 Tim. 2:5, 6)
Jesus was originally in heaven, "but he emptied himself and took a slave’s form and came to be in the likeness of men." (Phil. 2:7) Jehovah God did this when He transferred the life of His Son Jesus to the womb of Mary. By means of God’s holy spirit, Jesus was born as a perfect human and was not under the penalty of sin. - Luke 1:35
By sacrificing, or giving up, his perfect life in flawless obedience to God, Jesus paid the price for Adam’s sin. Jesus thus brought hope to Adam’s offspring. - Romans 5:19; 1 Corinthians 15:21, 22
By means of Jesus’ ransom sacrifice, we can receive “the forgiveness of our sins.” (Colossians 1:13, 14) We also have the hope of everlasting life on a paradise earth: “The wages sin pays is death, but the gift God gives is everlasting life by Christ Jesus our Lord.” (Rom. 6:23)
For more, see
The Ransom—God’s Greatest Gift
Living Forever—Is It Possible? You Can Live Forever
Life Beyond the Grave - It Is Possible!
What Happens After You Die?