The Holy Spirit guarantees that the Christian will never be removed from the family.

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.  

Not only does the Spirit testify that believers are God's Children (Rom 8:16), but He guarantees that they will never be removed from the family.Moreover, He ensures their future resurrection unto life.As Romans 8:11 explains "If the Spirit of Him who raised Jesus from the dead will also give life to your mortal bodies through His Spirit who dwells in you"

- John MacArthur

Strange Fire: The Danger of Offending the Holy Spirit with Counterfeit Worship p.193