The scriptures are the work of the Holy Ghost because they are inspired by Him. The words recorded of Jesus are His words, but the recording of these words is truly the work of the Third Person of the Blessed Trinity. The only time that we know of when Jesus wrote, was when He wrote in the sand. The recording of some of what Jesus said and did was written down by others, specifically the Evangelists: Saint Matthew, Saint Mark, Saint Luke, and Saint John. We know that there was much more that Jesus said and did, but they could not record everything. The Evangelists each wrote for very specific purposes. Usually, they wrote for the instruction or edification of specific people. Or that we may know that Jesus is truly God made Man. Under the inspiration of the Holy Ghost, these writers recorded what was deemed necessary, useful or beneficial for the goal they had in writing.
There were many other written accounts or "gospels" that were written by other authors. The Church (guided by the Holy Ghost) has looked into all of these and has labeled them as apocrypha. They could not be proven to have been inspired by the Holy Ghost, and therefore, were not acceptable as Sacred Texts and were not included in the Bible. Today with the flood of "information" on the internet, these apocrypha are often easily accessed and shared (especially by non-Catholics or those who wish to accuse the Church of hiding and deceiving others). But, even if you were to include these, we still would not have a written account of all that the Son of God has said and done. These uninspired texts are often found to be in contradiction to the inspired Sacred Texts, or to contain errors or heresies. Even if they were without these difficulties, they are generally not worth the time or effort to read because we should rather devote greater time and effort with those Texts that are without any doubt inspired by the Holy Ghost and are therefore Sacred.
The Sacred Texts themselves are often twisted by misguided or even perverted minds that seek to find justification for their sinful lives. When confronted by such individuals, we are reminded that even the devils can quote scriptures. The many false "Christian" religions have often taken the Sacred Texts (that the Church has preserved), and "edited" them to suit their own ends. Frequently deleting large sections, or re-translating passages that they wish to make prove or confirm their own personal heresies. A favorite idea among these people is that of "private interpretation." This practice opens up the Sacred Texts to every conceivable error, heresy, and sin.
God has foreseen and given us a defense against this abuse of the Holy Bible. The Holy Ghost has been given to the Church and lives within Her, guiding and protecting Her. She is the official and therefore the only true interpreter of these works. If we desire to know what God is telling us in the Sacred Scriptures, we must turn to the Church to find out, how to understand what is written. Those who have broken away from the Church and began their own religions have rejected the Church's teaching in favor of their own private interpretation. In rejecting the Church's teaching, they have rejected, not men, but rather God. They have denied the Holy Ghost. Of course they will deny this and claim to be individually guided by the Holy Ghost. In this, they would have the Holy Ghost to contradict Himself in the necessarily confused and contradictory interpretations that "private interpretation" creates. Hence they create a multiplicity of gods in opposition to the One True God.
It is only in the True Church that we find an infallible teacher of the Word of God. Every other "interpreter" is subject to error, confusion, and even heresy and sin. The Catholic Church has the protection and guidance of the Holy Ghost. Hence, it is only in the Catholic Church that we can find the true teachings of Christ, and therefore, salvation. There is no salvation outside the Catholic Church because it is only within Her that the Holy Ghost shows us the True Christ; and teaches us how we must live; as well as give us the means (Grace) to live according to the Will of God.