This time our line of reasoning derives from the Spirit’s work in the life of believers. In Christ’s promise to the disciples that He would send the Spirit, He specifically states that the Spirit would abide with them forever (John 14:16). This is surely a significant statement.
Paul assured the Ephesian believers that the Spirit in us is a guarantee that we will in actual fact attain our inheritance. Here is how he put it: 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. (Ephesians 1:13-14 ESV) He further states that the Spirit is the seal of our redemption (Ephesians 4:30).
Those familiar with Old Testament history will know that throughout many times of Israel’s history there was very little true worship. At one point Elijah thought he was the only true worshiper of God left. Because the Spirit abides in God’s people, it is impossible that there should cease to be a “remnant.” In fact, Paul says as much: So too at the present time there is a remnant, chosen by grace. (Romans 11:5 ESV)
In the very context of Election, Paul asserts that “the gifts and the calling of God are irrevocable” (Romans 11:29 ESV). This is an extremely profound statement. It means that once God has called someone to Himself and granted them the Holy Spirit, He will never revoke it. Bear in mind that election is not coextensive with covenant. Just because someone was in the covenant community of Israel, it was not an iron-clad guarantee that this person was also elect unto salvation. This is why Paul mentions the “remnant.”
In short, the Spirit’s abiding work in the lives of believers is a proof of the doctrine of the Perseverance of the Saints. The Spirit abides eternally in those He has sealed. His work is irrevocable and permanent. Therefore those who are sealed cannot apostatize and will most certainly be saved.