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."

 It is characteristic of Jewish style to say things twice, the second way explaining and amplifying the first. Any verse of the Psalms will show us this Jewish habit of what is technically known as parallelism: 