Ephesians 1:13-14 In him you also, when you heard the word of truth, the gospel of your salvation, and believed in him, were sealed with the promised Holy Spirit, who is the guarantee of our inheritance until we acquire possession of it, to the praise of his glory.
The gospel of our salvation is the word of truth. It is a message that must be heard; and it is a message that must be believed. When a person hears the gospel, and believes upon Jesus, they are sealed with the promised Holy Spirit.
In ancient times, a sealed message was authenticated as a word of truth if it had a wax seal. The seal was the sign that the message was truly from the one who sealed it.
When a person hears the message of Jesus, and believes upon him; he or she is sealed with a stamp that is more authentic then a wax seal. The seal is none other than the Holy Spirit; the third member of the trinity. And when the third member sets his seal upon you; when he takes up residence inside your heart, you begin to take on the characteristics of the one who placed his seal upon you. You start to bear the fruits of repentance, the fruits of the Spirit (love, joy, peace, patience, kindness, gentleness, and self control), and bear the armor of God. The seal shows us that we are Gods. It shows others that we are Gods. And it one day will show Jesus at the last judgement that we belong to his Father.