The hope of eternal life is not left to chance, it is a definite thing that can be known by the possessor as is evidenced by the Word of God.
Assurance of an inward witness: Romans 8:16
Assurance given by the Holy Spirit: 1 John 4:13
Assurance is evident by new love for Christians: 1John 3:14
Assurance is evident by new life: 2 Corinthians 5:17
Assurance, a result of believing: 1 John 5:13