Question
What is the gospel? (the "good news" of the Bible, the core Christian message)
Analysis
The oldest summary of the message
1 Corinthians 15:3–1 Corinthians 15:5 is widely regarded as an early creed Paul received and passed on: Christ died for our sins, was buried (proving He was truly dead), was raised on the third day (proving death was defeated), and appeared to many witnesses. Paul stakes everything on the resurrection being real: if Christ was not raised, he says, the preaching and the faith are empty (1 Corinthians 15:14; 1 Corinthians 15:17). So the gospel is first a set of historical events about Jesus, not primarily advice or moral instruction.
Why it is 'good news'
The good news answers a problem the Bible has already named: 'all have sinned and fall short of the glory of God' (Romans 3:23), and sin earns death (Romans 6:23). The gospel is that God Himself acted to rescue: 'God proves His love for us in this: While we were still sinners, Christ died for us' (BSB, Romans 5:8). Salvation is therefore a gift, 'by grace you have been saved through faith… not by works, so that no one can boast' (BSB, Ephesians 2:8; Ephesians 2:9), received by trusting Christ, not by earning God's favor (Romans 6:23, second half). The prophets pictured this long before: the herald who announces peace and salvation brings 'good news' (Isaiah 52:7).
The response and the reach
The gospel calls for repentance and faith (Mark 1:15; Acts 20:21) and confessing Jesus as the risen Lord (Romans 10:9). It is meant for all nations: Jesus sent His followers to carry it everywhere (Matthew 28:19; Mark 16:15), and Peter declares 'there is salvation in no one else' (Acts 4:12). Jesus also framed the same message as the arriving kingdom of God (Mark 1:15; Luke 4:43), the King has come, and His death and resurrection open the door in.