A Roman seal conveyed authenticity, security, ownership, and authority. And the Spirit of God represents those same realities in the lives of His children. Those who have received the Holy Spirit can rest assured that they are truly saved (authenticity) and that their salvation can never be lost or stolen from them (security). Moreover, the Spirit’s presence in their lives demonstrates that God is their Lord and Master (ownership). As they are led by the Spirit, they will manifest a life of submissive obedience to Christ (authority). All this is part of the Spirit’s sealing work.
John MacArthur