A seal is that which authenticates or ratifies, that which makes fast or secure, that which gives full assurance to a transaction. A seal is an engraved stamp used to impress or seal a letter, either to claim it as the property of the one, who seals it; or as authorizing the one to whom it is addressed as alone entitled to break it. The Great Seal of the United Kingdom, for instance, is that which authenticates, and makes binding the laws of the British constitution.
Scripture affords us instances of the use of seals.
" The Pharisees came together unto Pilate, saying... Command therefore that the sepulcher be made sure until the third day... so they went, and made the sepulcher sure, sealing the stone, and and setting a watch " (Matt. 27:62-6662Now the next day, that followed the day of the preparation, the chief priests and Pharisees came together unto Pilate, 63Saying, Sir, we remember that that deceiver said, while he was yet alive, After three days I will rise again. 64Command therefore that the sepulchre be made sure until the third day, lest his disciples come by night, and steal him away, and say unto the people, He is risen from the dead: so the last error shall be worse than the first. 65Pilate said unto them, Ye have a watch: go your way, make it as sure as ye can. 66So they went, and made the sepulchre sure, sealing the stone, and setting a watch. (Matthew 27:62‑66)).
Woe betide anyone who would dare to tamper with these seals, but when the One, who seals is God, who is omnipotent, omniscient, and omnipresent, the sealing is eternally effective, and no power in heaven, earth, or hell can tamper with it.
It is clear that the sealing is that aspect of the Holy Spirit's indwelling in which God is pleased to claim the believer for Himself once and forever with a claim that is everlasting. The believer is " Sealed unto the day of redemption " (Eph. 4:3030And grieve not the holy Spirit of God, whereby ye are sealed unto the day of redemption. (Ephesians 4:30)), that is till the coming of the Lord to take His own in a moment, in the twinkling of an eye. If a saint has died in the meantime, he will be raised at the second coming of our Lord, and given a body like unto Christ's.
The question may be asked, when is the believer sealed?