It could easily be argued that the true words of Allah can not be changed or deleted in any way.
The Qur’an states many times that Allah’s words have been said and recorded plainly so that there can be no confusion. The source is reliable, plain and cannot be changed!
It can be also argued that people can change the interpretation, omit or distort words at will to suit their own agendas.
It can also be said that people are not perfect and things become less clear over time. For mankind using its own strength, the further their origin and its goals are to the present day, the more likely their vision will wander from their original intentions. This being said the following Hadith says it all really:
Jami at-Tirmidhi 2653:-
We were with the Prophet when he raised his sight to the sky, then he said, “This is the time when knowledge is to be taken from the people, until what remains of it shall not amount to anything.”
So Ziyad bin Labid al-Ansari said: “How will it be taken from us while we recite the Qur’an? By Allah we recite it, and our women and children recite it.”
He said: “May you be bereaved of your mother, O Ziyad! I used to consider you among the Fuqaha of the people of Al-Madinah. The Torat and the Injil are with the Jews and Christians, but what do they avail of them?”