Now that you know God: Christians have a relationship with God like a child with a parent, not like a slave with a master (4:5–7).
how is it that you are turning back? Paul was confused that Christians would want to return to their old life of spiritual slavery (4:19–20).
are known by God: God is the one who saves and has taken the initiative in understanding their souls and forgiving them freely (Psalm 139:1–6, 23–24; Luke 2:34–35; Hebrews 4:12).
By turning back to circumcision (as a way of being accepted by God), the Galatians would be returning to the same useless spiritual principles they knew when they worshiped false gods. Both ways of living required people to work hard to please a demanding master who was never satisfied.