You are mine

Further more, you who heard the message of the truth, the Good News offering you deliverance, and put your trust in the Messiah were sealed by Him with the promised Ruach Hakodesh, who guarantees our inheritance until we come into possession of it and thus bring Him praise commensurate with His glory.
Ephesians 1:13,14


Sealed- sphragizo
Put His seal on you - identified you as His own .
Mark with a seal:
For preservation, protection from satan.

In order to prove, confirm, or attest a thing:
to confirm , authenticate, place beyond doubt.
to prove one's testimony to a person that he is what he professes to be