The Apostles' Creed is thought to be the earliest formal Christian statement of belief, which the later Nicene Creed (AD 381) expanded. It is unlikely that the twelve apostles actually created and circulated this creed among the churches of God, as its origins are second century, but the Apostles' Creed is an early confirmation of what a majority of professing Christians believed in the first few centuries of the church's existence.
(As an aside, a glaring detail missing from the Apostles' Creed is any claim of Trinitarianism; it reads simply, in Latin, "Credo in Spiritum Sanctum"—"I believe in the Holy Spirit." The later Nicene Creed adds Personhood and the title "the Lord, the giver of life" to the Holy Spirit, as well as equality in worship and glory with the Father and Son. This is an indication that the Trinity doctrine was formulated and accepted by the Catholic Church in the fourth century and is not original to biblical Christianity.)
By far, the bulk of the Apostles' Creed concerns Jesus Christ:
I believe in Jesus Christ, [God the Father's] only Son, our Lord.
He was conceived by the power of the Holy Spirit and born of the Virgin Mary.
He suffered under Pontius Pilate, was crucified, died, and was buried.
He descended to the dead. On the third day He rose again.
He ascended into heaven and is seated at the right hand of the Father.
He will come again to judge the living and the dead.
Central to the doctrine of Christianity is the resurrection of Christ from the dead. An even earlier, biblical statement by the apostle Paul attests to this fact:
For I delivered to you first of all that which I also received: that Christ died for our sins according to the Scriptures, and that He was buried, and that He rose again the third day, according to the Scriptures, and that He was seen by Cephas, then by the twelve. (I Corinthians 15:3-5)
Even earlier, the apostle Peter's first sermon builds to its crescendo of the good news of the resurrection of Jesus from the dead and what it means:
[David], foreseeing [that his descendant, Messiah, would sit on his throne], spoke concerning the resurrection of the Christ, that His soul was not left in Hades, nor did His flesh see corruption [Psalm 16:10]. 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. . . . Therefore let all the house of Israel know assuredly that God has made this Jesus, whom you crucified, both Lord and Christ. (Acts 2:31-33, 36)
We can go back even further, to Christ's ministry itself. Jesus gave only one sign to verify His Messiahship, and it was His resurrection from the dead. The scribes and Pharisees had demanded a sign from Him to prove His claims. He responded:
An evil and adulterous generation seeks after a sign, and no sign will be give to it except the sign of the prophet Jonah. For as Jonah was three days and three nights in the belly of the great fish, so will the Son of Man be three days and three nights in the heart of the earth. (Matthew 12:39-40)
In harmonizing the four gospel narratives—of which about a quarter concerns His arrest, trial, crucifixion, and resurrection—it is clear that this sign was fulfilled to the very second. He rose from the dead exactly three days and three nights—seventy-two hours—from His burial "in the heart of the earth." The amazing point about this is that, being dead, He had no power to effect either His burial or His resurrection! Far from being a "mere coincidence," it is proof that God the Father, in His sovereignty, brought this sign to pass in its every detail.
Doctrinally, why is His resurrection so vital to Christian belief? Beyond the fact that it fulfilled the sign, the resurrection of Jesus Christ opened the way to eternal life and glory for those who believe. While the sinless Jesus' crucifixion and death paid for all the past sins of those who accept Christ's blood for their forgiveness, it leaves them redeemed but without a future. A dead Savior leaves salvation incomplete. As the apostle Paul explains in I Corinthians 15:14, 19: "If Christ is not risen, then our preaching is empty and your faith is also empty. . . . If in this life only we have hope in Christ, we are of all men the most pitiable."
Yet, by raising Jesus from the dead, restoring His glorious spirit-body, and exalting Him to His right hand, the Father made possible two crucial realities:
Jesus became our Mediator and High Priest before the Father, giving us the opportunity to have a relationship with Him (Hebrews 8:6; 10:12-13, 19-22). Paul tells us, "For through [Christ] we both [Jews and Gentiles] have access by one Spirit to the Father" (Ephesians 2:18). As Jesus Himself says, "I am the way, the truth, and the life. No one comes to the Father except through Me" (John 14:6).
Jesus became "the Firstborn among many brethren" (Romans 8:29) and "the firstborn from the dead" (Colossians 1:18; Revelation 1:5). By overcoming death through the resurrection from the dead, He became the Archegos—the Forerunner, the Trailblazer—for everyone who faithfully follows Him as a disciple (Hebrews 2:10-16). Paul writes:
But now Christ is risen from the dead, and has become the firstfruits of those who have fallen asleep [died]. For since by man came death, by Man also came the resurrection of the dead. For as in Adam all die, even so in Christ all shall be made alive. But each one in his own order: Christ the firstfruits, afterward those who are Christ's at His coming. (I Corinthians 15:20-23)
In this way, the resurrection from the dead is mankind's God-given "victory through our Lord Jesus Christ" over death, the last enemy (I Corinthians 15:57, 26). It provides us great comfort to know that death is but a step in God's plan to give eternal life to us in His Kingdom (Hebrews 9:27-28). Paul's reassuring words in I Thessalonians 4:14, 17 assert the Christian hope: "For if we believe that Jesus died and rose again, even so God will bring with Him those who sleep in Jesus. . . . And thus we shall always be with the Lord."