“...you were sealed with that Holy Spirit of promise.”
What does it mean to be “sealed”? The moment you receive Jesus Christ as your Lord and Savior, the Holy Spirit of God seals you into Himself. That seal marks you as a child of God. You cannot lose your salvation and you belong to God for all time and eternity. When you are sealed, you are His!
Second Timothy 2:19 says, “Nevertheless the solid foundation of God stands, having this seal: 'The Lord knows those who are His.'” You are sealed into a relationship with God by the Holy Spirit.