As an orthodox Christian, I believe that Jesus is, and has always been, the Second Person of the Trinity, fully God, and Creator of all things. I find these most-explicitly taught in the Gospel of John. The main thing that divides Christians and Jehovah's Witnesses is that they deny all of those things. I have addressed their interpretation of John 1:1 here. Now, I want to deal with their distortions of the "I Am" verses later in the Gospel.
In chapter 8, Jesus is involved in a controversy with the Pharisees. They claim that their descent from Abraham guarantees their spiritual welfare. His response is well-known (John 8:58): “Truly, truly, I say to you, before Abraham was, I am.” He is referring to Exodus 3:14, in which God tells Moses that His name is I Am (the name "Yahweh," anglicized as "Jehovah," is a form of the Hebrew verb "to be"). He was claiming to be the God of Abraham come in the flesh. And the Pharisees understood His reference, because they immediately picked up stones to kill Him for blasphemy.
In the New World Translation, the Bible version published by the Jehovah's Witnesses, Jesus's words have been altered to, "Before Abraham came into existence, I have been." They have altered the tense of the verb ("ego eimi" in the Greek) to eliminate the connection to Exodus. In addition to the blatantly self-serving nature of that paraphrase, it also shows the lie in the Watchtower's claim to believe in, and teach, the Bible.
Moreover, this doctrinal error invokes the lesser-known words earlier in the passage.
In John 8:24, Jesus tells the Pharisees, "I told you that you would die in your sins, for unless you believe that I Am, you will die in your sins.” In many versions, you will find "I am he." "He" isn't in the original, which is why the NASB and KJV, for example, print it in italics. I have left it out, because I think it weakens the thrust of His words. But look closely at what He says: if a person denies "that I am," that is, that He is Jehovah our Savior, then that person will die in his sins, to be denied eternal life. The NWT has this verse reading, "If you do not believe that I am the one, you will die in your sins." Witnesses should ask the Watchtower this question: If "ego eimi" should be past tense in verse 58, then why not also in verse 24, part of the same portion of narrative?
This controversy between Christians and Jehovah's Witnesses is not a mere quibble over a couple of words. Eternity is at issue. I personally do not wish Witnesses to face eternal death because of a deception. My hope is that they will see this, and that the Holy Spirit will work repentance in their hearts (II Timothy 2:25), that they may receive the same eternal life that I have.