Punishment is very different from discipline.
As children of our Heavenly Father, we are promised that He will never punish us. That does not mean that He is not concerned with sin or evil in our lives.
Punishment, by its very nature has the goal of creating hurt or harm in some way as a consequence for wrong doing. All the punishment that we deserve was placed on Jesus when He died on the cross. As a result, God will never punish those who trust in Jesus Christ.
Does that mean that He will not discipline us? On the contrary, God disciplines those whom He loves. Hebrews 12:11 states that discipline, "produces a harvest of righteousness and peace for those who have been trained by it.” God lovingly uses discipline to turn His children from their sin. Discipline is never intended for harm.
This difference between punishment and discipline is demonstrated in this story of a doctor who spoke honestly with a young boy about the treatment he was about to receive.