What does it mean that the believer is sealed with the Holy Spirit?

Sealing is a symbol of ownership and security. It is often used today to authenticate documents, or as an assurance and guarantee. God puts His stamp of ownership on the believer today by giving the believer the gift of the Holy Spirit. So true is this that we read in Romans 8:9 that "if any man have not the Spirit of Christ, he is none of His." This sealing takes place automatically when one believes in Christ as is made plain from the verse in Ephesians 1:13: "In whom ye also trusted, after that ye heard the word of truth, the gospel of your salvation: in whom also after that ye believed, ye were sealed with the Holy Spirit of promise." Sealing also implies security as is seen from Ephesians 4:30: "And grieve not the Holy Spirit of God, whereby ye are sealed unto the day of redemption." The day of redemption refers to that time when we will be in heaven. Then not only will our souls be redeemed but also our bodies (Romans 8:23). So the believer is sealed for the day of redemption. The sealing by the Holy Spirit is the believer's assurance or guarantee that he or she will be in heaven with Christ.