How can a merciful God punish you ?
Law of compensation
I am (God) a formless, birthless, deathless and a merciful spirit created by light

How can a merciful spirit punish mankind?
You punish yourself through evil actions or free yourself through right actions
However you (man) are accountable for my (God)

Law of attraction
Law of humanity and and the Law of action (Karma)
which is collectively called as the Law of Nature