Nicodemus comes to Jesus by night. They discuss the nature of man's origin. Nicodemus asked how anyone is able to know these things himself.
John 3:15 That whosoever believeth in him should not perish, but have eternal life.
John 3:15 that everyone who believes may have eternal life in him.
[...being lifted up is necessary for the Son of the man.]...because every one believing in him should possess life perpetual.
The KJV is misleading because it appears to be talking about the future but Jesus is talking only about a possibility "might have" or "should have."
The phrase is the KJV, "not perish but" was added in the Latin Vulgate, but not part of the original Greek.
"Everlasting" is an adjective based on the word that means "age" or "eon." It has the sense of "perpetual" or "ageless."
The word translated as "life" means "living" but it also means "substance", "existence," and "property." Christ uses it to mean "existence" beyond physical life. See this article on the various Greek words that Jesus uses to describe various aspects of life.
Jesus saw trust in him as leading to perpetual life, but the reference is to his death and resurrection,
- MW - Missing Word -- The word "the" before "believeth" is not shown in the English translation.
- WF - Wrong Form - The "believeth" is not an active verb but a participle, "believing."
- OS -- Outdated Source -- The Greek word translated as "not perish, but" existed in the KJV Greek source but not the source we use today.
- WW - Wrong Word -- The word translated as "who" should be something more like "one."
- WF - Wrong Form - The "believes" is not an active verb but a participle, "trusting."
- WP -- Wrongly Placed -- The word "in" phrase doesn't appear here but after "trusting."
That -- The word translated as "that" is an adverb "in that place," "there," "where," "when," or as a conjunction that starts a subordinate clause "that," "when," "in order that" or "because."
whosoever -- The word translated as "all" is the Greek adjective meaning "all," "the whole," "every," and similar ideas. When it is used as a noun, we would say "everything."
missing "the" -- (MW) The untranslated word is the Greek definite article, which usually precedes a noun and, without a noun, takes the meaning of "the one." The Greek article is much closer to our demonstrative pronouns ("this," "that," "these," "those"). See this article for more.
believeth -- (WF) The Greek word translated as "believeth" does not apply to religious belief as much as it does trusting in other people, especially their word. Christ usually uses it in contexts, as the one here, that apply to trusting words. The word is a particle, not an active verb.
in " -- The word translated as "in" means "in," "within," "with" (an instrument), "during" (time), or "among" with a dative object as the one here.
him - The word translated as "him" is the Greek word commonly translated as third-person pronouns in English.
should -- This helping verb in English comes from the form of the Greek verb that indicates a possibility. We would usually say "might" or "should" in English.
not perish, but -- (OS) There is nothing in the Greek that can be translated as "not perish, but" in the source we use today but it does exist in the source that the KJV translators used.
have -- The word translated as "have" means to "have," "possess," "bear," "keep close," "have means to do," "to have due to one," or "keep" and many specific uses.
eternal -- "Everlasting" is an adjective based on the word that means "age" or "eon." It has the sense of "perpetual" or "ageless."
life. -- The word translated as "life" means "living" but it also means "substance," "existence," and "property." Jesus uses it to mean "existence" beyond physical life. For more on how Christ uses this word with other words about human existence (soul, heart, spirits, etc.), read this article.
That -- The word translated as "that" is an adverb "in that place," "there," "where," "when," or as a conjunction that starts a subordinate clause "that," "when," "in order that" or "because."
everyone -- The word translated as "everyone " is the Greek adjective meaning "all," "the whole," "every," and similar ideas. When it is used as a noun, we would say "everyone" in the singular masculine.
missing "who" -- (WW) The word translated as "who" is the Greek definite article, without a noun, it has the sense of "the one." The Greek article is much closer to our demonstrative pronouns ("this," "that," "these," "those") than the English "the." See this article for more.
believes -- (WF) The Greek word translated as "believes" does not apply to religious belief as much as it does trusting in other people, especially their word. Christ usually uses it in contexts, as the one here, that apply to trusting words. The word is a particle, not an active verb.
may -- This helping verb in English comes from the form of the Greek verb that indicates a possibility. We would usually say "might" or "should" in English.
have -- The word translated as "have" means to "have," "possess," "bear," "keep close," "have means to do," "to have due to one," or "keep" and many specific uses.
eternal -- "Everlasting" is an adjective based on the word that means "age" or "eon." It has the sense of "perpetual" or "ageless."
life. -- The word translated as "life" means "living" but it also means "substance," "existence," and "property." Jesus uses it to mean "existence" beyond physical life. For more on how Christ uses this word with other words about human existence (soul, heart, spirits, etc.), read this article.
in " -- (WP) The word translated as "in" means "in," "within," "with" (an instrument), "during" (time), or "among" with a dative object as the one here.
him - The word translated as "him" is the Greek word commonly translated as third-person pronouns in English.
ἵνα [134 verses](adv/conj) "That" is hina, which means "in that place", "there", "where", "when", "that", "in order that", "when," and "because."
πᾶς [212 verses](adj sg masc nom) "Whosoever" is from pas (pas), which means "all", "the whole", "every", "anyone", "all kinds," and "anything."
ὁ [821 verses](article sg masc nom) Untranslated is the Greek definite article, hos, ("the").
πιστεύων [69 verses](part sg pres act masc nom) "Do you...believe" is pisteuo, which means "to trust, put faith in, or rely on a person," "to believe in someone's words," "to comply," "to feel confident in a thing," and "to entrust in a thing."
ἐν [413 verses](prep) "In" is en, which means, with a dative object, "in," "on," "at," "by," "among," "within," "surrounded by," "in one's hands," "in one's power," "during," and "with." With the accusative, it means "into," "on," and "for." Referring to time, it means. "in the course of" or "during."
αὐτῷ [720 verses](adj sg masc dat) "Him" (adj sg masc acc) "Him" is autos, which means "the same," and the reflexive pronouns, "myself," "yourself," "himself," "herself," "itself," or the oblique case of the pronouns, "him," "her," and "it." It also means "one's true self," that is, "the soul" as opposed to the body and "of one's own accord." In the adverbial form, it means "just here" or "exactly there."
ἔχῃ [181 verses](3rd sg pres subj act) "Shall have" is echo, which means "to have," "to hold," "to possess," "to keep," "to have charge of," "to have due to one," "to maintain," "to hold fast," "to bear," "to carry," "to keep close," "to keep safe," and "to have means to do."
ζωὴν [42 verses](noun sg fem acc) "Life" is zoe, which means "living," "substance," "property," "existence," and, incidentally, "the scum on milk." It has the sense of how we say "make a living" to mean property. Homer used it more to mean the opposite of death.
αἰώνιον [23 verses](adj sg fem acc) "Everlasting" is aionios, which means "lasting for an age," "perpetual," and "eternal." From "aion" which is used in the bible to mean an "age." -- "Everlasting" is an adjective based on the word that means "age" or "eon." It has the sense of "perpetual" or "ageless."