The Holy Spirit SEALS the Believing sinner.

The Believer is sealed by the Holy Spirit

2Co 1:22  and He has also set His seal upon us, and has put His Spirit into our hearts as a pledge and foretaste of future blessing.

Who hath also sealed us - The word used here (from σφραγίζω  sphragizō) means to seal up; to close and make fast with a seal, or signet; as, e. g., books, letters, etc. that they may not be read.

It is also used in the sense of setting a mark on anything, or a seal, to denote that it is genuine, authentic, confirmed, or approved, as when a deed, compact, or agreement is sealed. it is thus made sure; and is confirmed or established. Hence, it is applied to persons, as denoting that they are approved, as in Rev_7:3; “Hurt not the earth, neither the sea, nor the trees, until we have sealed the servants of our God in their foreheads;” compare Eze_9:4; see the note, Joh_6:27, were it is said of the Saviour, “for him hath God the Father sealed;” compare Joh_3:33.

We are sealed by the Holy Spirit

In a similar manner Christians are said to be sealed; to be sealed by the Holy Spirit Eph_1:13; Eph_4:30; that is, the Holy Spirit is given to them to confirm them as belonging to God. He grants them His Spirit. He renews and sanctifies them. He produces in their hearts those feelings, hopes, and desires which are an evidence that they are approved by God; that they are regarded as his adopted children; that their hope is genuine, and that their redemption and salvation are sure - in the same way as a seal makes a will or an agreement sure. God grants to them His Holy Spirit as the certain pledge that they are His, and shall be approved and saved in the last day. In this there is nothing miraculous, or in the nature of direct revelation.

Eph 1:13  And in Him you Gentiles also, after listening to the Message of the truth, the Good News of your salvation--having believed in Him--were sealed with the promised Holy Spirit;

Eph 1:14  that Spirit being a pledge and foretaste of our inheritance, in anticipation of its full redemption--the inheritance which He has purchased to be specially His for the extolling of His glory.

Matthew Henry: “7. The seal and earnest of the Spirit are of the number of these blessings. We are said to be sealed with that Holy Spirit of promise, Eph_1:13. The blessed Spirit is holy himself, and he makes us holy. He is called the Spirit of promise, as he is the promised Spirit. By him believers are sealed; that is, separated and set apart for God, and distinguished and marked as belonging to Him.”
****************************************