Ephesians 1:13b  ….in whom also, having believed, you were sealed with the Holy Spirit of promise.

The Greek word for seal is sphragis which means signet (W.E. Vine). A signet was used to imprint softened wax on a letter or document. The impression made by such a seal identifies the owner of the signet.

Then the king commanded, and they brought Daniel, and cast him into the den of lions.  Now the king spake and said unto Daniel, Thy God whom thou servest continually, he will deliver thee.  And a stone was brought, and laid upon the mouth of the den; and the king sealed it with his own signet, and with the signet of his lords; that the purpose might not be changed concerning Daniel.  Daniel 6:16&17

MacArthur’s study notes on Ephesians 1:13&14 say that a seal represents authenticity, authority, ownership and security. Other study helps usually mention at least two of these four representations.

If something is authentic, it is true and genuine.  Not just anyone can issue a law, declaration or edict.  In ancient times a document or letter that carried the imprint of the king or governor’s signet was understood to be true, genuine, and binding.  

II Timothy 2:19 states; the firm foundation of God standeth, having this seal, The Lord knoweth them that are His. The Lord Jesus Himself says; My sheep hear my voice and I know them and they follow me.  Followers of Christ, as evidenced by their love and obedience to His written word, are authentic (true and genuine) Christians.

The king or governor’s edicts were backed by the authority given him by either a greater sovereign or by the power of military force. When the slaughter of the Innocents was ordered by the paranoid King Herod, there was not much that could be done about it.  King Herod’s authority was backed by the power of Rome.  Had an uprising occurred, King Herod most likely would have ordered the slaughter of all who opposed him.

Now he which stablisheth us with you in Christ, and hath anointed us, is God; Who hath also sealed us, and given the earnest of the Spirit in our hearts (II Corinthians 1:22&23).  And Jesus came and spake unto them, saying, All power (authority) is given unto me in heaven and in earth (Matthew 28:18).  

Believers are sealed in Christ.  C.I. Scofield mentions in his notes that the Holy Spirit Himself is the believer’s seal.  The sealing of believers is accomplished in, through and by the highest authority, that of God Himself.

Concerning ownership; What? know ye not that your body is the temple of the Holy Ghost which is in you, which ye have of God, and ye are not your own? (I Corinthians 6:19)

The verb form to seal also carries the ideas of preservation, safe keeping and safe delivery (W.E. Vine).  When something is secure, it is surrounded by strength.  

Now the next day, that followed the day of preparation, the chief priests and Pharisees came together unto Pilate, Saying, Sir, we remember that that deceiver said , while he was yet alive, After three days I will rise again.  Command 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. Pilate said unto them, Ye have a watch: go your way, make it as sure as ye can.  So they went, and made the sepulchre sure, sealing the stone, and setting a watch (Matthew 27:62-66).  

In this passage the word translated as sure in the KJV is translated as secure in the NKJV.  The securing of Messiah’s tomb was accomplished by sealing the stone and setting a guard.

In this case the security was only temporary, in the case of the believer the security is eternal.  And grieve not the holy Spirit of God, whereby ye are sealed unto the day of redemption (Ephesians 4:30).  

To be secure is to be surrounded by strength.  To be surrounded by strength is to be without a care.  Are you sealed and secure in Christ?  

Note: If the Holy Spirit (who is God) is God’s signet then He is the believer’s seal.  The impression made by such a seal identifies the owner of the signet.  Whose image is it that we bear?