Few questions in life are more fundamental than these: “Can I know that I have eternal life and could I ever lose it?” Fortunately, the Bible provides clear answers to these questions and the basis of my assurance.
Eternal Life is a Gift
It is very clear that eternal life is a gift. Note Jesus’ statement to the Samaritan woman: “If you knew the gift of God, and who it is who says to you, ‘Give Me a drink,’ you would have asked Him, and He would have given you living water.” He later states: Whoever drinks of this water [from the well] will thirst again, but whoever drinks of the water that I shall give him shall never thirst. This clearly indicates eternal security. For if a person could ever lose eternal life he would obviously thirst again. No amount of works (either before or after believing) can earn eternal life.
Eternal Life is Permanent
It is very evident that eternal life is permanent. For example, Jesus states: “I am the bread of life. He who comes to Me shall never hunger, and he who believes in Me shall never thirst.” He also said: “For I have come down from heaven, not to do My own will, but the will of Him who sent Me. This is the will of the Father who sent Me, that of all He has given Me I should lose nothing, but should raise it up at the last day.” Eternal life is a forever gift, appropriated once-and-for-all by faith. The moment I believe I am eternally secure – based on the promises of God.
Assurance of Eternal Life
I am assured of my salvation through the promises of God. Jesus states: “Most assuredly, I say to you, he who hears My word and believes Him who sent Me has eternal life, and shall not come into judgment, but has passed from death into life.” Thus, at the moment of faith, I have eternal life, I am assured that I will never be judged for my sins and I have already begun my new life in Christ. God’s word also assures me that I can know that I have eternal life: These things I have written to you who believe in the name of the Son of God, that you may know that you have eternal life, and that you may continue to believe in the name of the Son of God. Note that assurance is not based on our works, but rather on the promises of God. Though eternal life can never be lost, my assurance of it may be. Thus it is important that we remain in God’s Word. Yes, I can be sure that I have eternal life - from the very moment I believe. “Most assuredly, I say to you, He who believes in me has eternal life.”
 The word δωρεά dorea used here means free gift. Other forms of this word are used in Eph. 2:8 and Rev. 22:17 to refer to eternal life.
 John 4:10.
 John 4:14. The original text reads “will by no means thirst forever.” That is, the need which this water meets can never recur.
 See Eph. 2:9, Rom. 3:9-20, Titus 3:5. Jesus never mentioned works to this woman.
 This is the strong Greek double negative οὐ μὴ ou me = never and is repeated in verse 37.
 John 6:35.
 John 6:38-39. This is also repeated in vs. 40. Note that the images of regeneration (John 3:3) and resurrection (John 5:25) are irreversible.
 Note also John 10:28-29 and John 11:25-26. The Greek actually says, not perish forever and not die forever.
 John 5:24. John 6:47, 20:31 and 1 John 5:1 are similar verses of assurance.
 1 John 5:13. The moment a person believes in Jesus as His Savior he has God’s witness (1 John 5:10), God’s Son, and eternal life (vs. 11-12) within him. The moment a person believes, he knows that he has eternal life.
 Note Rom. 4:5. This is not to say that there will not be good works in the life of each believer in Christ. It is simply saying that works are not the basis of my assurance.
 My assurance stops if I stop believing the promises of God. One example would be John the Baptist (Luke 7:19). The Galatians also lost their assurance because of false teachers who taught that one must be saved by keeping the law of Moses (Gal. 1:6-7; 3:1-3).
 John 8:31-32, 15:4-8.
 John 6:47.