God seals us with the Holy Spirit, as believers in the Lord Jesus Christ. "In Him (Christ) you also trusted, after you heard the word of truth, the gospel of your salvation; in whom also having believed, you were sealed with the Holy Spirit of promise" (Ephesians 1:13). Those who truly believe the gospel of Christ have been sealed by the Holy Spirit.
In Bible days, legal documents were sealed to guarantee the authority of transactions. Scripture uses this as an illustration to guarantee believers that we are God's people. The Holy Spirit is the seal of God, giving us the right to be called a child of God (John 1:11-12).
God seals us, when we believe the gospel of Christ. That's the New Testament promise of God to every believer. As believers, we have been sealed with the Holy Spirit as our Guide, Counselor, Helper and Comforter. The seal of the Spirit is for each and every believer in the Lord Jesus Christ.
The Holy Spirit seals us, when we are saved by grace through faith in Christ. It happens to each believer upon trusting in Christ (Ephesians 1:13-14). It is the guarantee or earnest of the Spirit, that true believers will be kept until the redemption of our bodies, at the Day of Christ (Ephesians 4:30).