You were marked in [Christ] with a seal, the promised Holy Spirit, who is a deposit guaranteeing our inheritance until the redemption of those who are God’s possession — to the praise of his glory. —Ephesians 1:13-14.
God is faithful to his word. He keeps his promises. But that faithfulness was not enough for him. He wanted us to have the full assurance of our future with him. So, he gave us a down payment, a deposit, so we could be sure of our inheritance and look forward to fully realizing our salvation. He had Jesus pour the Holy Spirit onto us as an anointing (Titus 3:3-7; 1 John 2:20, 27) and into us as a guarantee of what is to come (2 Corinthians 1:22, 5:5). When God buys us out of slavery to our mortal bodies and redeems us into our eternal home with bodies that will not grow old or decay, we won’t need the deposit; we will have our complete inheritance. But until then, until we go to him, we rejoice in the amazing truth that he makes his home within us!