All human beings fall short of the minimum standard of good under God's justice. They are all deserving of judgment. Christians believe that judgment was carried out on Christ. Under discipline, the recipient is the object of love. Since the goal is the betterment of the recipient, discipline is related to conditions in the person's life, not to acts of wrongdoing per se.
Justice looks to the past to ascertain whether the punishment fits the crime.
Discipline looks toward the future to determine whether the actions will help the recipient improve. Justice cannot refuse to punish one who deserves it. Discipline is free to react to any action on the part of the recipient in the way which will be most beneficial. This could include doing nothing in some situations. Justice would never act to punish one who has done no wrong.