Seal
A manufacturer puts a seal on its product as a guarantee of the product's freshness or fine craftsmanship. In the same way, God puts a seal on his followers as proof that we permanently belong to him. This seal is the Holy Spirit (see Holy Spirit), who guides us and brings us understanding of God's ways. God's seal on our lives affects our actions, showing that our lives are accountable to God.

Seals are also used for security measures, keeping the prying eyes from gaining secret information. God, for unexplained reasons, has kept some information about the end of this world sealed up; he did this by commanding the prophets not to write down what they were seeing. In the book of Revelation, we read that God unleashes calamities that are kept under seven seals in heaven. Only Jesus Christ is allowed to open these seals.

When we become Christians, God puts his seal––the Holy Spirit––on our lives, proving we belong to him.
2 Corinthians 1:22; 5:5
Ephesians 1:13-14
Jesus' tomb is sealed and heavily guarded. His resurrection and escape from the sealed tomb are proof of his divinity.
Matthew 27:66
Knowledge about the end of the world has been sealed up, so we don't understand all the prophecies now.
Daniel 8:26
Revelation 10:4
The book of Revelation tells us that only Jesus will be able to open the seven seals. These seals will unleash plagues on the earth.
Revelation 5:1–8:5