The Holy Spirit plays a large role with respect to our eternal security. Paul teaches us this truth in Ephesians 1:13-14. He writes, “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.” Yes, through the Holy Spirit, we are signed, sealed and delivered into our inheritance and we’re just waiting for the acquisition. Eugene Peterson, in The Message, translates these two verses like this: “It’s in Christ that you, once you heard the truth and believed it (this Message of your salvation), found yourselves home free—signed, sealed, and delivered by the Holy Spirit. This signet from God is the first installment on what’s coming, a reminder that we’ll get everything God has planned for us, a praising and glorious life.”
As the third person of the God Head, one primary function of the Holy Spirit is our sealing. Fruchtenbaum says, “The Holy Spirit does seal, and the purpose of the sealing is to seal up the believer in Christ so that he can never fall out. The clear emphasis is that the believer has been sealed, not just temporarily, not just until he no longer believes, but has been sealed unto the day of redemption. Having been sealed, the final redemption is guaranteed. Perhaps the sealing ministry of the Spirit is the most vital one, emphasizing eternal security.” Later in Ephesians 4:30, Paul exhorts us to be responsive to the Holy Spirit in our lives, “… by whom (The Holy Spirit) you were sealed for the day of redemption.”
A. W. Tozer writes, “Upon God’s faithfulness rests our whole hope of future blessedness. Only as He is faithful will His covenants stand and His promises be honored. Only as we have complete assurance that He is faithful may we live in peace and look forward with assurance to the life to come.” Knofel Staton adds to Tozer’s thinking. He writes, “Our future rests upon God’s faithfulness. God is always dependable, while we may not be at times. While the Corinthians were not being trustworthy, God kept His trustworthiness. When we face setbacks, God is faithful. When we face guilt, God is faithful. When the bank account goes, God is faithful. When a loved one dies, God is faithful. When we know we have been faithless, God is faithful.”