Why does 1 John say Christians are unable to sin? The verse in question, 1 John 3:4 (HCSB)

Everyone who commits sin also breaks the law; sin is the breaking of law. You know that He was revealed so that He might take away sins, and there is no sin in Him. Everyone who remains in Him does not sin; everyone who sins has not seen Him or known Him.
Little children, let no one deceive you! The one who does what is right is righteous, just as He is righteous. The one who commits sin is of the Devil, for the Devil has sinned from the beginning. The Son of God was revealed for this purpose: to destroy the Devil’s works. Everyone who has been born of God does not sin, because His seed remains in him; he is not able to sin, because he has been born of God. This is how God’s children — and the Devil’s children — are made evident.

but earlier, in 1 John 1:10, he seemingly says the opposite

If we say, “We don’t have any sin,” we make Him a liar, and His word is not in us.

In many other places, it is made clear that Christians are not made righteous by their own works and that we are not without sin, rather we are forgiven of sin and are made righteous by God's grace and Jesus' salvation. Why does 1st John 3:4 say otherwise? Am I missing the point?
Why does 1 John say Christians are unable to sin?


  1 John 3:6  Whosoever abideth in him sinneth not: whosoever sinneth
  hath not seen him, neither known him. 
  
  1 John 3:9  Whosoever is born of God doth not commit sin; for his seed
  remaineth in him: and he cannot sin, because he is born of God.


One of the problems in translating something between languages is that if a word in one language carries more information in it than the other language can handle in one word, information can be lost.

For example in 1 John 3:9 the word "commit" is "poieō" in Greek which can mean commit, cause, perform, continue. However the word also carries with it additional information in that the verb is present, active, indicative.

Other translators would say something like "Whoever is born of God does not habitually commit sin."

The word "sinneth" in verse six is "hamartanō" and has the same "present, active, indicative" verb construction and can also be rendered, "Whosoever abideth in him does not habitually sin".

While there are many good English translations, it is sometimes necessary to go to the original language to find information that may not have been brought fully into the English.