The seal of the Spirit is God’s mark upon those who belong to Christ: by giving them His Spirit, God identifies them as His own and guarantees the inheritance He will complete in them.
A seal marks ownership and secures a promise. When a person believes, he is sealed with that Holy Spirit of promise, who is the earnest — the down payment — of the inheritance until the redemption of the purchased possession. The Spirit’s presence is both God’s stamp of ownership and His pledge that He will finish what He has begun.
See in Scripture: 2 Corinthians 1:22; Ephesians 1:13–14; Ephesians 4:30; Romans 8:23