A lot has been written on the subject of the apostasy. Yet I would like to look at it from a Biblical point.
The apostle Paul notes the changing of doctrine that had been occurring in Galatia:
"I marvel that you are so soon removed from him that called you to the grace of Christ, to another gospel: Which is not another; but there be some that trouble you, and would pervert the gospel of Christ." Galatians 1:6-7
Paul further mentions the divisions that were already occurring in the break-up of the church in Corinth at that time:
"Now I implore you, brothers, by the name of our Lord Jesus Christ, that you all speak the same thing, and that there be no divisions among you; but that you be perfectly joined together in the same mind and in the same judgment. For it has been told to me regarding you, my brothers, by them which are of the house of Chloe, that there are contentions among you. Now this I say, that every one of you says, I am of Paul; and I of Apollos; and I of Cephas; and I of Christ. Is Christ divided? was Paul crucified for you? or were you baptized in the name of Paul?" 1 Corinthians 1:10-13
Paul states later to them:
"Now in this that I'm declaring to you I don't praise you, you are coming together not for the better, but for the worse. For first of all, when you come together in the church, I hear that there are divisions among you; and I partly believe it." 1 Corinthians 11:17-18
When writing to Titus Paul said in regard those in the church:
"For there are many unruly and vain talkers and deceivers, especially those of the circumcision." Titus 1:10
"... Paul also according to the wisdom given to him has written to you; As also in all his epistles, speaking in them of these things; in which are some things hard to be understood, which they that are unlearned and unstable wrest, as they do also the other scriptures, to their own destruction." 2 Peter 3:15-16
The apostle Paul presented that the members of the church at his time shouldn't regard that Christ had come yet. He points out that a falling away of the church had to come first:
"We are requesting of you, brothers, regarding the coming of our Lord Jesus Christ, and us gathering together to him, That you don't soon be shaken in mind, or be troubled, neither by spirit, nor by word, nor by letter as from us, as that the day of Christ is here. Let no man deceive you by any means: for that day shall not come, except there come an apostasy [Greek - apostastasia] first, and that man of sin be revealed, the son of perdition; Who will oppose and exalt himself above all that is called God, or that is worshipped; so that he sets himself up in the temple of God, proclaiming himself to be a God. ... And now you know what is being presently held back, that when his time comes he might be revealed. For the mystery of iniquity is already working: only he who now holds back [God] will hold back, until he [God] is removed from it [altogether]. And then shall that Wicked one be revealed, whom the Lord shall consume with the spirit of his mouth, and shall destroy with the brightness of his coming: Even him, whose coming is after the working of Satan with all power and signs and lying wonders." 2 Thessalonians 2:1-9
Here Paul has presented that no one should regard that Christ will be coming until the church falls away and the true God is removed from it. Also that God is holding it back from happening at that point. He states that in charge of the apostate church one will arise claiming to be a God on earth. This latter prophesy could have been regarded as having being fulfilled not long after this time by Roman emperors or by the Pope.
Pope Pius V said, "The Pope and God are the same, so he has all power in Heaven and earth." quoted in Barclay, Cities Petrus Bertanous Chapter XXVII: 218.
"He [the Pope] can pronounce sentences and judgments in contradiction to the rights of nations, to the law of God and man...he can free himself from the commands of the apostles, he being their superior, and from the rules of the Old Testament...The Pope has power to change times, to abrogate laws, and to dispense with all things, even to the precepts of Christ." Decretal de Translat. Episcop. Cap.
Furthermore Paul is presenting that this "wicked one" will still be here when Christ comes again for Christ to "destroy [him] with the brightness of his coming". So this rules out Roman emperors, only leaving the Pope.
When writing to Timothy, Paul again mentions the fact that the church will lose its truth:
"For the time will come when they will not endure sound doctrine; but after their own lusts shall they heap to themselves teachers, having itching ears; And they shall turn away their ears from the truth, and shall be turned to fables." 2 Timothy 4:3-4
This had to be speaking of the church as a whole, as people are always creating false teachers.
So a complete moving away from the truth has been in the beginning of its action at the time just after Christ; and has eventually occurred fully. Some truths remained through the publication of the Bible. But a lot of this was distorted by the ideas men had come to accept as truth. This is why it was necessary for the truth to be restored to mankind once again by revelation from God himself. God has set up his Church upon the earth again. It was set up by revelation, as in New Testament and Old Testament times. This means that people can be assured that the true ordinances of God are being performed in the right way, and a source of the whole truth is available to all. This is the purpose of the Church of Jesus Christ of Latter-Day Saints.