Sealing

Concise Bible Dictionary:

2. Believers are sealed by the Spirit for the day of redemption, and the Spirit is also the earnest of their inheritance (2 Cor. 1:2222Who hath also sealed us, and given the earnest of the Spirit in our hearts. (2 Corinthians 1:22); Eph. 4:3030And grieve not the holy Spirit of God, whereby ye are sealed unto the day of redemption. (Ephesians 4:30)). The gift of the Spirit is the seal. This could not be until redemption had been wrought and righteousness secured thus for man. But the seal is now the distinctive mark of those who are of God. The idea of sealing is distinct from that of being born of the Spirit, as well as from that of being led of the Spirit after He has been received. Believers only are sealed, in virtue of their faith in a Savior who died for them and rose again. The sealing, based on forgiveness of sins, gives the consciousness of the benefit gained by faith.
Various incidents in the Acts of the Apostles throw light upon this. On the day of Pentecost, after Peter had proclaimed the death, resurrection, and exaltation of Christ, the hearers being “pricked in their heart,” said, “What shall we do?” Peter replied, “Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins, and ye shall receive the gift of the Holy Ghost” (Acts 2:3838Then Peter said unto them, Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins, and ye shall receive the gift of the Holy Ghost. (Acts 2:38)). So also when Peter preached to Cornelius and those gathered with him, while he was saying “Whosoever believeth in Him shall receive remission of sins....the Holy Ghost fell on all them which heard the word” (Acts 10:43-4443To him give all the prophets witness, that through his name whosoever believeth in him shall receive remission of sins. 44While Peter yet spake these words, the Holy Ghost fell on all them which heard the word. (Acts 10:43‑44)). In Ephesians 1:1313In whom ye also trusted, after that ye heard the word of truth, the gospel of your salvation: in whom also after that ye believed, ye were sealed with that holy Spirit of promise, (Ephesians 1:13), it is said of the Gentiles that having believed the gospel of their salvation they were sealed. See HOLY SPIRIT.

“420. Impressions of Seals” From Manners and Customs of the Bible:

The bricks of Egypt, Babylonia, and Assyria boar marks which have evidently been made with a seal. Egyptian wine jars and mummy pits were sometimes sealed with clay. There have been found in Assyria public documents made of clay, and having the letters stamped in them, and the marks of official sealing. In the East, doors of granaries or of treasure rooms are to this day sometimes sealed with clay, so that it is impossible to enter without first breaking the seal. The sepulcher of Christ was probably sealed in this way. See note on Matthew 27:6666So they went, and made the sepulchre sure, sealing the stone, and setting a watch. (Matthew 27:66) (#735). Clay is used in preference to wax because the former hardens with the heat, while the latter melts. The engraving represents a lump of clay from Assyria, having several impressions of seals upon it.

“797. Sealing” From Manners and Customs of the Bible:

Burder (Oriental Customs, No. 1120) suggests that there may be an allusion here to the sacrificial death of Christ, and cites from Herodotus an account of the ceremonies accompanying the selection of a victim for sacrifice among the ancient Egyptians. If, after careful search, the animal was found without blemish, the priest bound a label to his horns, applied wax to the label, and sealed it with his ring. This set it apart for sacrifice, and no animal could be offered unless thus sealed. We have no knowledge of any such ceremony among the Jews, though they were careful in selecting their victims; but the sacrificial customs of other nations were doubtless known to them. The meaning of the text may; therefore, be, that Jesus bad been set apart or “sealed” as a sacrifice in order that he might obtain eternal life for those who believe on him.
On the other hand, Lightfoot interprets the passage to mean that God had confirmed Jesus by his seal to be “the great Ruler both of his kingdom and family”; and he refers for illustration to a rabbinical form of instruction which declares the seal of God to be Truth, one of the names which Jesus applies to himself. See John 14:66Jesus saith unto him, I am the way, the truth, and the life: no man cometh unto the Father, but by me. (John 14:6). Compare also John 3:3333He that hath received his testimony hath set to his seal that God is true. (John 3:33).