In the ancient world the seal was of great importance.  When making a seal - a special ring would be used to make an impression on melted wax.  When a thing was sealed it provided:

1- Identification of the Authority of he who left the mark

2 - It showed Possession of the thing or document which was sealed

3 - A seal also authenticated the contents as being genuine.

4 - Protection was also clear as the improper breaking of the seal meant incurring the full legal wrath of the one whose seal was broken

Two seals in scripture are worth noticing:

First, Pilate had Jesus Tomb Sealed to keep Jesus body in the Grave – this Seal was broken based upon the Higher authority of God almighty.

Second: in the Revelation 5 John weeps because no one is able to open the 7-sealed scroll which contains the plan of God.  Jesus then takes the scene and is, alone, qualified to open that which God has sealed.

This gives great insight to Ephesians 1:13 which tells us:

In Him (Jesus) you also trusted, after you heard the word of truth, the gospel of your salvation; in whom also, having believed, you were sealed with the Holy Spirit of promise…