Christians always say that they believe in the Holy Spirit as the guider to the truth as Jesus said:
Joh 14:26 But the Comforter,
even the Holy Spirit, whom the Father will send in my name,
he shall teach you all things, and bring to your remembrance all that I said unto you.
As it is written about the function of the Holy Spirit:
In Christian theology Holy Spirit is believed to perform specific divine functions in the life of the Christian or the church. The action of the Holy Spirit is seen as an essential part of the bringing of the person to the Christian faith.
[48] The new believer is “born again of the Spiritâ€.
[49] The Holy Spirit enables Christian life by dwelling in the individual believers and enables them to live a righteous and faithful life.
[48] The Holy Spirit also acts as comforter or
Paraclete, one who intercedes, or supports or acts as an advocate, particularly in times of trial. And it acts to convince the unredeemed person both of the sinfulness of their actions, and of their moral standing as sinners before God.
[50] Another faculty of the Holy Spirit is the inspiration and interpretation of scripture. The Holy Spirit both inspires the writing of the scriptures and interprets them to the Christian and/or church.[51]
http://en.wikipedia.org/wiki/Holy_Spirit_(Christianity)
So if all Christians believe that the Holy Spirit teaches the inspiration and interpretation of scriptures, why do Christians have that vast diversity among them in both aspects?
Let’s talk first about inspiration, till now there is a diversity between Catholics and Protestants about the number of books of the Bible, as the Catholics have 73 books, Protestants have 66 only and believe that others are apocrypha. Ethiopian and Coptic churches have even more books.
If we looked at the New Testament, although its canon has been settled now, but actually this wasn’t the case among early church fathers. There have been some books as epistle of Barnabas, Shepherd of Hermas that were accepted by many fathers, now they are not in the NT canon. On the other hand, some of the books accepted now as second epistle of Peter, book of Hebrews and book of Revelations, this link can be a nice list made telling about the disputed books:
http://www.bible-researcher.com/canon5.html
If we are talking about Bible interpretations then we can see the diversity in faith among Christian churches, some of them are like having statues and images of saints, belief in Mary whether it is the mother of the Lord or not, immaculate conception, Holy Spirit himself who is supposed to guide Christians, Christians have diversity whether he is proceeded from the Father only or the Father and the Son, and here we go.
Even among early church fathers as well, there have been many misinterpretations and opinions that are against Christian theology although Christians consider them as orthodoxy church fathers who fought heresy, and believe they had a role in proving the NT true by quoting verses in their books. Actually these orthodoxy fathers adopted non orthodoxy opinions, and this can be shown more in my article concerning church fathers and Bible preservation:
http://jesus-is-muslim.net/church-fathers-bible/
The question now is; if the Holy Spirit actually guides Christians, Why didn’t he guide the early fathers? Either he guided them and they rejected, this means that they are no more orthodox as they reject the Holy Spirit. Or that he didn’t guide them, which negates what Christians believe in the Holy Spirit guidance. If the Holy Spirit guides all Christians, why do we see many Christian sects? Yes many Christians among different sects believe their sect is the only true one, this question may not apply to them, but the first question still applies. Other Christians who believe the diversity among sects is not something major or believe to be non-denominational may need to have an answer to this question as well as the first question.
So when Christians say that they are guided with the Holy Spirit, the answer shall be: which one?