When you believed, you were marked in him with a seal, the promised Holy Spirit, who is a deposit guaranteeing our inheritance until the redemption of those who are God’s possession.  (Ephesians 1:14)

To those ‘sealed’ as God’s possession, based on gospel faith, there is a deposit that acts as a guarantee of inheritance within His kingdom.  The word ‘deposit’ translates the Greek noun ἀρραβών (arrabón) meaning a down payment or surety; the first instalment of a payment to be redeemed in full at a later date.