13 In Him 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,
14 who is the guarantee of our inheritance until the redemption of the purchased possession, to the praise of His glory.
The Holy Spirit is God’s guarantee that we belong to him and that he will do what he promised. The Holy Spirit is like a down payment, a deposit. The presence of the Holy Spirit demonstrates the genuineness of our faith, proves that we are God’s children and secures eternal life for us. His power works in us to transform us now.