Why does the Holy Qur'an state that Jesus death was prophesied (I will cause you to die, raise you to me)? 3:55.Does this not prove that Christ was not killed accidentally?Did he not die in accordance with the will of God?When was the Trinity started?If all the bible is not true then how is someone to know what parts to believe?

Praise be to Allah, the Lord of the World; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

1) Jesus Christ was neither killed nor crucified, but Allah raised him with his body and soul unto Him. He will descend from the Heavens as a harbinger or a sign that the Day of Judgment is imminent or approaching. A number of verses in the Holy Qur'an prove this fact as follows:
Allah Says (interpretation of meaning): {…but they killed him not, nor crucified him, …} [4:157]. He Says: {And there is none of the people of the Scripture (Jews and Christians), but must believe in him ['Isa (Jesus), son of Maryam (Mary), as only a Messenger of Allâh and a human being], before his ['Isa (Jesus) or a Jew's or a Christian's] death. …} [4:159]. He also Says: {And he ['Isa (Jesus), son of Maryam (Mary)] shall be a known sign for (the coming of) the Hour (Day of Resurrection) [i.e. 'Isa's (Jesus) descent on the earth]. …} [43:61].
A number of Hadith of the Prophet Muhammad (Sallallahu Alaihi wa Sallam) in this regard are reported in the Books of Hadith.
The verse which reads: {I will take you and raise you to Myself …} [3:55] is interpreted by some scholars as evidence that Jesus was taken from the earth, and not killed.
2) The pure source of the Christian message is the divine revelation from Allah the Almighty to Jesus . The early faithful disciples and adherents of this religion in the Qur'an are called (Nasara). This nomenclature might be derived either from Nazareth, the city where Jesus was born or because they supported Jesus when he asked them for help as mentioned in the Holy Qur'an: {Said the Disciples, "we are Allah's helpers".} [61:14].
Later the term "Christians" was widely used to include all those who claimed to be the followers of Jesus . Christianity has its roots in Judaism, as Jesus was a messenger of Allah to the children of Israel (The Jews) for the revival of the true religion revealed to Moses and to rectify the alterations made by the Jews in the Scriptures. Allah Says (interpretation of meaning): {And Allah will teach him the Book and Wisdom, The Torah and the Gospel., And appoint him A Messenger to the children of Israel ..etc.} [3:48].
Within three centuries after Jesus was sent as a Messenger to the Jews, too many alterations were made in the Bible. The faithful Apostles of Jesus were persecuted by the Jews, for half a century. The people began to write their own invented Gospels (e.g. the Gospel according to St. Mark or St. Luke) with different versions, which were far from the original teachings of Jesus . Each author of the various Gospels and epistles claimed that he was the chosen instrument to bring the message of Jesus to the Gentiles.
The doubtful apocrypha sometimes are not included in the old Testament. The Injeel of Jesus was lost, and its authenticity was at stake.
In 325 AD, the first largest congregation of the Christians was held under the patronage of the Roman king Augustine in which the doctrine of trinity was finally formulated. Trinity in Christian theology means that God exists as three persons - the Father, Son and Holy Spirit - who are united in one substance or being. This doctrine is a mixture of pagan, Judaism, and atheistic concepts. They allege that Jesus is the son of God, and the Holy Spirit refers to the Spirit breathed by Allah into Maryam (Mary). Allah Says (interpretation of meaning): {Surely, disbelievers are those who said: "Allah is the third of the three (in a Trinity)". But there is no Ilah (god) (none who has the right to be worshipped) but One Ilah (God-Allah). …..} [5:73] He also Says: {Surely, they have disbelieved who say: "Allah is the Messiah [Isa (Jesus)], son of Maryam (Mary)". …} [5:72].
3) No doubt that so many alterations were inserted in the original scriptures (the Gospel or Bible). Here we will give one example of the so many verses of the Holy Qur'an in this regard: {Then woe to those who write the Book with their own hands and then say, "This is from Allah", to purchase with it a little price! Woe to them for what their hands have written and woe to them for that they earn thereby.} [2:79].
Some portions of the Old Testament and the New Testament may be in tact, but we cannot ascertain which is which in the long time process of alterations. Muslims should believe in the original scriptures revealed to Moses and Jesus in general. Even if the books of the Bible were not fabricated, after the advent of Islam they were revoked and set aside by the Holy Qur'an, the Final Divine Revelation revealed to Prophet Muhammad (Sallallahu Alaihi wa Sallam).
However, the fabricated Books of the Bible are classified by the Muslim scholars into three categories as follows:
(a) The portions which are in conformity with what we have been informed by the Qur'an and Sunnah, and this should be accepted by Muslims and they have to believe in it.
(b) The portions which are contradictory to what we have been informed by the Qur'an and Sunnah, and this should be rejected by the Muslims and they should not believe in it.
(3) The portions which are neither in conformity nor contradictory to what we have been informed by the Qur'an and Sunnah (i.e. no reference has been made to it in the reliable Islamic sources). In this case, the Muslims should neither believe nor annul the same because it may be true or false.
However, it can be narrated as an anecdote to learn lessons from it. The Prophet Muhammad (Sallallahu Alaihi wa Sallam) in a Hadith narrated by al-Bukhari said to his companions: "It is permissible to relate any story about the children of Israel" . [ Abu Dawood and Ahmad ].
The Prophet Muhammad (Sallallahu Alaihi wa Sallam) also said: "You should neither believe nor annul whatever is related by the children of Israel. Say we believe in Allah and His Messengers". If it is false you do not believe in it, and if it is true you do not nullify it" . [ al-Bukhari ].
Allah knows best.