In my opinion justice is more important in social life because justice ensures order in society. If thére is ño justice, there will be chaos in society. Evil minded people will create disorder. Devine justice is equally important because human justice may not always be perfect and its scope is limited to legal matters and not to moral matters. Breaking of moral law is punished by Devine justice or the Law of Karma (action).
Mercy should be shown to a person who accepts his mistakes and repents and promises not to repeat the mistake again, otherwise not. But in criminal cases, when court has to set an example before the society, they usually do not show mercy. However, mentally, we can pardon everybody who has hurt us to purify ourselves. There also the concept of devine mercy when God or the Unknown or the Ultimate reality Himself grants mercy on sincere repentence.
Justice is superior in the material world whereas mercy is superior in the spiritual world.
