If the Son ... - The Son of God - heir of all things - who is forever with God, and who has therefore the right and power to liberate men from their thraldom.
Shall make you free - Shall deliver you from the bondage and dominion of sin.
Free indeed - Truly and really free. You shall be blessed with the most valuable freedom; not from the chains and oppressions of earthly masters and monarchs, but from the bondage of sin.