Seals: Appropriation of Saints to God by the Spirit
Source: TTT
2 Corinthians 1:22
placed His seal on us, and put His Spirit in our hearts as a pledge of what is to come.
Ephesians 1:13
And in Him, having heard and believed the word of truth—the gospel of your salvation—you were sealed with the promised Holy Spirit,
Ephesians 4:30
And do not grieve the Holy Spirit of God, in whom you were sealed for the day of redemption.