Why are there so many Christian denominations? Unsaved friends complain that the multiplicity of church denominations turns them off. Are some denominations better than others?
You ask two questions. In some, perhaps most, cases, the answer to the first question lies in sinful human nature, expressing itself in contrary ways. A church split can be caused by carnal leaders who are careless about the "faith once for all delivered to the saints" (Jude 3). Opposing them are believers who refuse to accept sloppy doctrine. Sooner or later irreconcilable disagreements about the meaning of Scripture lead to a church split and church splits havein the pastled to the formation of new denominations.
Some divisions become virtually unavoidable and may be said to be good. They happen because the people in control have given up critical elements of doctrine. Conscientious, well-instructed members are determined to contend for the apostolic faith. New denominations tend to emphasize the doctrine being ignored or twisted in church from which they secede. Baptist churches emerged from churches that baptized infants; Pentecostal churches from groups that did not pay enough attention to the Holy Spirit, etc. Of course, due to space restrictions, this is a very simplified description.
Which denomination is the best? If your friend is a serious person, he will not be offended by differences; instead, he will be amazed by the similarities, especially the almost universal adherence to the great, historic creeds. Sooner rather than later, your friend will find a company of brothers and sisters with whom he shares a common life in Christ, and a common creed.