Assurance of eternal life comes from trusting in Jesus Christ as Lord and Savior, believing in His finished work on the cross.
Eternal life is promised to those who believe in Jesus Christ. John 3:36 states that whoever believes in the Son has eternal life, while those who do not obey the Son will not see life. This assurance is rooted in the belief that God's word is true and that Christ's sacrifice is sufficient for the atonement of sin. Romans 10:9 reinforces this assurance by stating that if you confess with your mouth that Jesus is Lord and believe in your heart that God raised Him from the dead, you will be saved. Therefore, faith in Christ guarantees our eternal security as it is rooted in His faithfulness.
Scripture References:
John 3:36, Romans 10:9, John 5:24
Commentary