Here the word "slave" is a metaphor. This implies that "sin" is like a master for the one who sins. AT: "is like a slave to sin" (See: [[rc://en/ta/man/translate/figs-metaphor]])
This is an ellipsis. You may translate it by including the implied words. AT: "the son is a member of the family forever" (See: [[rc://en/ta/man/translate/figs-ellipsis]])
# if the Son sets you free, you will be truly free
Jesus speaks of himself in the third person. "Free" here is an idiom for the ability to do as one desires. AT: "if you allow me to set you free, you will truly be free" or "if the Son gives you the ability to do as you desire, you will truly be able to do as you desire" (See: [[rc://en/ta/man/translate/figs-123person]] and [[rc://en/ta/man/translate/figs-idiom]])