Notice what happens once we come to faith: We are 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 (Eph 1:13-14). Despite the certainty of our inheritance, we don’t possess it yet. God’s Spirit serves as a down payment. Paul told the Romans, “The Spirit himself bears witness with our spirit that we are children of God, and if children, then heirs—heirs of God and fellow heirs with Christ” (Ro 8:16-17).
The Spirit with all of the fruits that grow from him is like the official seal on an important document. He testifies to our security in Christ. He makes it known that we belong to God.
The word guarantee in the Greek once referred to earnest money. It was a literal down payment. If a man wanted to secure something that he intended to buy, he would make a down payment. It was a commitment, a pledge that said, “Don’t you worry. I’ll be back to pay the rest and pick up my property.”
God makes that same pledge with his Spirit. God guarantees us that we will receive our full inheritance as his adopted children. To think of it another way, the Spirit is the engagement ring on the finger of Christ’s bride.