The seal given by God as a guarantee of His promise is the
Holy Spirit.
Specifically, this concept is most clearly articulated in the New Testament, in the writings of the Apostle Paul. Here are a few key verses:
* Ephesians 1:13-14: "In him you also, when you heard the word of truth, the gospel of your salvation, and believed in him, were sealed with the promised Holy Spirit, who is the guarantee of our inheritance until we acquire possession of it, to the praise of his glory."
* 2 Corinthians 1:21-22: "And it is God who establishes us with you in Christ, and has anointed us, and who has also put his seal on us and given us his Spirit in our hearts as a guarantee."
* Ephesians 4:30: "And do not grieve the Holy Spirit of God, by whom you were sealed for the day of redemption."
These verses (and others) suggest that:
* When someone believes in Jesus Christ and accepts the Gospel, they receive the Holy Spirit.
* The Holy Spirit is a *seal*, signifying ownership and security. God has marked believers as belonging to Him.
* The Holy Spirit is a *guarantee* (or earnest/down payment) of the full inheritance and blessings that God has promised to believers, including eternal life and full redemption.
* This sealing is a work of God, not something we earn.
In summary, the Holy Spirit is the seal and guarantee of God's promises to those who believe in Jesus Christ.