The divided nature of Christianity means that the Bible cannot be God's Word.

Fields rightly points out that there are divisions in Christianity.  However, these divisions are direct violations of Christ's prayer in John 17:11, 21, 22.  Christ did not want divisions, but wanted all his followers to be one, just as the Father and the Son are one.  Jesus knew that unity would help the spread of the gospel:

20 "I do not ask for these only, but also for those who will believe in me through their word, 21  that they may all be one, just as you, Father, are in me, and I in you, that they also may be in us, so that the world may believe that you have sent me. John 17:20-21 (ESV)

Paul clearly commanded those early Christians not to have divisions among them (1 Cor 12:25), but they should rather " united in the same mind and the same judgment." (1 Cor 1:10; Phil 1:27; 2:2)  In an effort to deal with division, Paul gives this command:

10 As for a person who stirs up division, after warning him once and then twice, have nothing more to do with him, 11 knowing that such a person is warped and sinful; he is self-condemned. Titus 3:10-11 (ESV)

So divisions in Christianity are sinful, and they are not the will of God.  In spite of this, Paul the apostle prophesied that divisions would come quickly into Christianity after his death:

29 I know that after my departure fierce wolves will come in among you, not sparing the flock; 30 and from among your own selves will arise men speaking twisted things, to draw away the disciples after them. Acts 20:29-30 (ESV)

Paul also prophesied the major hallmarks of that coming apostasy:

1 But understand this, that in the last days there will come times of difficulty. 2 For people will be lovers of self, lovers of money, proud, arrogant, abusive, disobedient to their parents, ungrateful, unholy, 3 heartless, unappeasable, slanderous, without self-control, brutal, not loving good, 4 treacherous, reckless, swollen with conceit, lovers of pleasure rather than lovers of God, 5 having the appearance of godliness, but denying its power. Avoid such people. 6 For among them are those who creep into households and capture weak women, burdened with sins and led astray by various passions, 7 always learning and never able to arrive at a knowledge of the truth. 8 Just as Jannes and Jambres opposed Moses, so these men also oppose the truth, men corrupted in mind and disqualified regarding the faith. 9 But they will not get very far, for their folly will be plain to all, as was that of those two men. 2 Tim 3:1-9 (ESV)

Peter also prophesied about the apostasy that would quickly come upon the church (2 Pet 2:1-21) and cause division.  Jude actually saw the fulfillment of Peter's prophecy (Jude 3-16).

Christianity was indeed united and faithful under the administration of the apostles of Christ.  That is not to say the churches were perfect and did not have problems (e.g., 1 Corinthians and Galatians), but the problems were worked out satisfactorily.  Church history indicates that the church remained faithful in most things when Roman persecution forced them into the catacombs.  Certain changes did occur during those 200 years in hiding, such as no longer requiring a plurality of elders, appointing one elder as a chief elder, substituting pouring for immersion baptism, etc.  Some of these changes were undoubtedly because their leaders were targeted by the Roman persecutions, and they had to practice their Christianity in secret or risk torture and death.  In 313 AD, Constantine the Great reversed the persecutions against the Christians, and by issuing his Edict of Milan, he proclaimed religious toleration throughout the Roman Empire.1

However, the freed church of the fourth century continued to change away from the pattern that we see in the Epistles.  The congregational governmental model  for the New Testament gave way to a Roman model.  By the time of the 6th & 7th centuries, that which came to be known as the "Catholic Church" (i.e., universal church) had lost any form of congregational government present in the first century, and instead there were bishops ruling over churches in an entire region, all of whom had equal authority.  However, the supremacy of the Roman Bishop was established over all other bishops, and became the papacy, thus fulfilling the Roman model of government.

Unfortunately, the drift of the Roman Catholic Church away from the Bible continued over the centuries, and differences arose between the Eastern church and the Western church.  A breach occurred in this relationship in 1054 AD, and the Eastern Orthodox Churches separated from the Roman Catholic Church.  This was the first major division in "Christianity," but it did not appear to lead the Roman church back to the Bible.  In 1517 a Catholic priest named Martin Luther, after reading a Bible, published his 95 Theses,2 and this started the Protestant Reformation.  The Catholic Church refused to be "reformed," so a whole host of protestant denominations then formed over the subsequent years.  This divisive movement has multiplied, and now there are literally thousands of denominations, many of which were started by a man or woman whose ultimate goal was to become rich from the collections of their members.

Thus, Fields has hit Christianity in our soft underbelly, in the place of ultimate shame that we want to keep hidden, and he is right that Christianity is divided, and he is right that this divisiveness has hurt Christianity severely.  Even worse, this divisiveness has hurt the credibility of Great Commission, and some people are not converted to Christ because Christianity is divided.

However, does this tragedy, this horrible sin, really prove that the Bible cannot be God's Word?  The Bible clearly records the prophecies that such divisions would occur, and that it would be sinful and unacceptable to God.  Therefore, the divisiveness of sinful man does not prove that the Bible is not the Word of God, because the Bible said it would happen.  In fact, the divisiveness in Christianity unwittingly confirms the Bible.