One who believes in the Son has eternal life, but one who disobeys{The same word can be translated "disobeys" or "disbelieves" in this context.} the Son won't see life, but the wrath of God remains on him."
An amazing example of the operation of this principle appears in the concluding words of this chapter.  The disciples of John the Baptist, who loved and honored him, and who believed what he said, nevertheless rejected Christ.  And why?  They were evil in themselves.