"Verily, verily, I say unto you, He that heareth my word, and believeth on him that sent me, hath everlasting life, and shall not come into condemnation; but is passed from death unto life." (John 5:24)]
"αλλα μεταβεβηκεν εκ του θανατου εις την ζωην", Their ‘passage over’ from death into life has already taken place,—from the state of spiritual death into that ζωὴ αἰώνιος, which in their believing state they ἔχουσι already. All those who have been truly "born-again" by God the Holy Spirit, are said to be "already passover" from spiritual death, to eternal life, which begins the moment the person is saved. "sealed by the Holy Spirit". So in Ephesians 1:13, "In him you also, when you heard the word of truth, the Gospel of your salvation, and believed in Him, were sealed with the promised Holy Spirit"
"Verily, verily, I say unto you, If a man keep my saying, he shall never see death" (John 8:51)
"θανατον ου μη θεωρηση εις τον αιωνα", literally, shall certainly not behold death for ever: i.e. shall never behold or experience death. The "born-again" believer has already passed spiritually from "death to life", after they are saved, and can never experience the "second death"
"And I give unto them eternal life; and they shall never perish, neither shall any man pluck them out of my hand" (John 10:28)
"και ου μη απολωνται εις τον αιωνα και ουχ αρπασει τις αυτα εκ της χειρος μου", . the use of the double negative in the Greek, "ου μη", is a very emphatic denial that those who have been given this eternal life, can "never, not ever, to the ages perish", and neither can anyone snatch them out of My Hand, and the next verse, "My Fathers Hand". Such is the eternal security of the believer. This is same promise that Jesus makes in John 11:25-26, "Jesus said unto her, I am the resurrection, and the life: he that believeth in me, though he were dead, yet shall he live: And whosoever liveth and believeth in me shall never die. Believest thou this?" > "shall never die", ου μη αποθανη εις τον αιωνα, "never, not ever, to the ages perish". the same double negative in the Greek, "ου μη", is used.
"unto an inheritance incorruptible, and undefiled, and that fadeth not away, reserved in heaven for you,
who by the power of God are guarded through faith unto a salvation ready to be revealed in the last time" (1 Peter 1:4-5)
"incorruptible", ἄφθαρτος, that is, eternal, immortal.
"guarded", which is, φρουρέω, describe the fortress in which or the garrison by which the Christian is guarded. And the One Who is gurading the believer, is ALMIGHTY GOD!