How is God both just and merciful?

How is it possible that God should be both God of justice and God of mercy?

God is just in that He visits no exceptional punishment upon any soul, which He has created.

He is just in that He has fixed immutable laws by which each individual must work upward to his own salvation.

Having fixed these laws from the beginning, which are exact, equitable and all-comprising, covering all the frailties and ignorance and blindness of humanity, He has clearly manifested his impartial justice in forming his laws so immutable that there can be no evading, ignoring, or overstepping them by anyone. 

They must be fulfilled and their conditions must be complied with, to the simplest factor.

No suffering, prayer, protestation or regrets—nothing can exempt the individual who has outraged the law from paying the penalty of that law.