What did early Christians believe that the resurrection showed?

Apparently early Christians believed that the resurrection showed that Jesus was God's physical son and that the concept of resurrection was more than metaphorical it was actually physical.

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The early Christians believed

the resurrection was the proof of the atoning character of the death of Christ, and of His Deity (Romans 1:4)

the resurrection was one of the characteristic features of the gospel, proving to the hearers the assurance of the divine redemption (1Corinthians 15:1-4; Romans 4:25)

the resurrection is regarded as the source and standard of the holiness of the believer. Every aspect of the Christian life from the beginning to the end is somehow associated therewith (Rom 6)

the resurrection was the guaranty and model of the believer's resurrection

(1 Corinthians 15). As the bodies of the saints arose (Matthew 27:52), so Christians are to be quickened (Romans 8:11), and made like Christ's glorified body (Philippians 3:21), thereby becoming spiritual bodies (1Corinthians 15:44), that is, bodies ruled by their spirits and yet bodies.

This a basic outline of New Testament teaching concerning the doctrine of the resurrection of Christ.