How does the soul fall from the spiritual world? What is the guarantee that we won’t fall again?

From: Mahesh

if jivatama is part and parcel of god why does it gets envious of God and come to this material world. if we were blissful serving god how can we develop envy towards him.

how can we say that once we go back to spiritual world we will never come back again to amterial world , when there is every chance that we can again become envious?