Jhn 3:15 That whosoever believeth in him should not perish, but have eternal life.
[...there was a need for the Son of man to be lifted high]...in order that all those believing in him might be possessing life eternal.
Explanation of Greek:
The KJV is misleading because it appears to be talking about the future but it is talking only about a possibility. This verse is just a dependent clause that completes the previous verse. In this verse, there is not "shall not perish" in the Greek sources that we used today. The phrase is used in the next verse (John 3:16), but it is not an absolute statement of what will happen.
The word translated as "shall have" means to "have", "possess", "bear", "keep close", "have means to do", "to have due to one", or "keep". It is in the present tense, subjunctive voice, not the future tense. The subjunctive indicates the possibility of something happening. The present has the sense of "might have now" or "might be possessing." The KJV consistently translated both the future tense and the subjunctive mood with the helper verb "shall" so the Bible is easy to misread.
The clause about "perishing" does not exist in the best Greek texts today or in recent translations such as NIV. It was an artifact of the KJV from its Textus Receptus source. The phrase was originally from the Latin Vulgate version. It does exist in John 3:16, but the form is again of possibility and the negative is one of thought or desire.
"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.
The phrase is directly saying the Christ was raised up in the past so that people now would have the possibilities of eternal life.
ὁ πιστεύων (part sg pres act masc nom) "Believeth" is from pisteuô (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."
αὐτῷ "Him" is from autos (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."
ἔχῃ (3rd sg pres subj act) "Shall have" is from echô (echo), which means "to have", "to hold", "to possess", "to keep", "to have charge of", "to maintain", "to hold fast", "to bear", "to keep close", "to keep safe," and "to have means to do."
ζωὴν "Life" is from zôê (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.