How does the relationship with the Holy Spirit assure salvation?

The relationship with the Holy Spirit is essential for assurance of salvation because He is the one who seals and marks believers as God's own. Ephesians 1:13-14 conveys that the Holy Spirit serves as the earnest or down payment for our inheritance until we fully enter into God’s promises. This sealing signifies that believers belong to God and assures them of their eternal security. Thus, the Holy Spirit empowers and sustains their faith, affirming that they will persevere to the end, as their salvation is upheld by God's divine authority through the Spirit's ministry.