What is the sealing referred to at Revelation 7:3?

Revelation 7:3 KJV
Saying, Hurt not the earth, neither the sea, nor the trees, till we have sealed the servants of our God in their foreheads.

let's define "seal" in the lexicon strong's concordance: G4972

Seal - Outline of Biblical Usage [?]
to set a seal upon, mark with a seal, to seal
for security: from Satan
since things sealed up are concealed (as the contents of a letter), to hide, keep in silence, keep secret
in order to mark a person or a thing
to set a mark upon by the impress of a seal or a stamp
angels are said to be sealed by God
in order to prove, confirm, or attest a thing
to confirm authenticate, place beyond doubt
of a written document
to prove one's testimony to a person that he is what he professes to be

scripture cross-references to "Rev 7:3", where it says, "till we have sealed the servants of our God in their foreheads" are below:

Revelation 14:1 KJV
And I looked, and, lo, a Lamb stood on the mount Sion, and with him an hundred forty [and] four thousand, having his Father's name written in their foreheads.

scripture cross-references to "Rev 14:1", where it says, "having his Father’s name written in their foreheads." are below:

Revelation 3:12 KJV
Him that overcometh will I make a pillar in the temple of my God, and he shall go no more out: and I will write upon him the name of my God, and the name of the city of my God, [which is] new Jerusalem, which cometh down out of heaven from my God: and [I will write upon him] my new name.

Revelation 7:3 KJV
Saying, Hurt not the earth, neither the sea, nor the trees, till we have sealed the servants of our God in their foreheads.

Revelation 13:16 KJV
And he causeth all, both small and great, rich and poor, free and bond, to receive a mark in their right hand, or in their foreheads:

Revelation 13:17 KJV
And that no man might buy or sell, save he that had the mark, or the name of the beast, or the number of his name.

Luke 12:8 KJV
Also I say unto you, Whosoever shall confess me before men, him shall the Son of man also confess before the angels of God:

References:

https://www.blueletterbible.org
Lexicon/Strong’s Concordance
https://www.quora.com

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