Sealed with the Spirit
“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.”
The seal in that era was recognized to represent ownership (when God seals a person with the Holy Spirit, he is marking that person as belonging to himself), security (when God seals a person with the Holy Spirit, it is as if he is saying, “This person belongs to me and is a member of my family and nothing can change that.”), and power (the seal of the Spirit brings with it the power of God - power that is greater than anything that is in this world, or even in the spiritual world).