What changed in Gandhi's views after the Amritsar massacre?

Christianity offered hope to people who wondered about the meaning of life in a harsh world.  It spoke of redemption and salvation that allowed people to endure hardship and suffering.  Those were some aspects of the Christian message's appeal.

Also, a big factor that convinced people in the Roman Empire of the value of Christianity was the way that Christians showed strength and character when they were being persecuted for their faith.  During the reign of Emperor Nero, Christians were persecuted heavily in Rome in the 60s AD. During the reign of Emperor Domitian in the 90s AD, there were further persecutions.  The bravery of Christians enduring persecutions made an impression on people, seeing them more as victims than as enemies of the state.