How do we know the doctrine of eternal salvation is true?

The doctrine of eternal salvation is rooted in God's unchanging promises, as seen in passages like Titus 1:2, which states that God promised eternal life before the world began. This covenantal relationship emphasizes that salvation is not contingent upon our actions but is secured by Christ's work and the faithful promises of God. Ephesians 1:3 elaborates on this by declaring that God has blessed us with all spiritual blessings in Christ, from eternity to eternity, confirming that believers are eternally safe in Him.