# Your throne ... is forever and ever

"Your kingdom ... is forever and ever" or "You will reign ... forever and ever" 

# Your throne, God

Possible meanings are that the word "God" 1) is a title for the king, who is God's representative or 2) modifies the word "throne" and means "Your kingdom that God has given you."

# a scepter of justice is the scepter of your kingdom

"you rule your kingdom with justice"