In the name of Allah , most gracious most merciful
It is very simple : they have the same origin ,they are revealed
by Allah.
If christians or jews find in Quran something similar to their book, they think this is a proof that Holy Quran is copied form ancient Bibles.
This is not true .But similarities to some Bibles are very normal.
But Quran is accurate and original in contrary to other books.
Quran teaches us that Turah and Bible (Tevrat and Inceel)
are given to prophets Moses and Jesus (peace be upon them)
and they were true revelations from God .If you find any
similarity between Quran and some sections of Gospels means
this parts are from the true revelation. Quran is revealed
to correct the holy books and to complete the religion of Allah.
Quran also teaches us that these Holy Books are corrupted in time.
And it is told this is made sometimes deliberately by some people or scholars.
Nobody can object this , since variations between gospels
are known by everybody .So nobody can be sure which part is from God allmighty.
You can search in google 'restore original bible' and find many
projects and documents containing plans how to restore original
bible .
To try to restore bible is like trying to restore a priceless antique
mosaic picture.Many parts of the mosaic are lost , replaced or broken .
This mosaic can look very good whith some restorations but it will never
be original.Noone can be sure which part is original .It is very
dangerous to claim everything in it is from God .
That is why scholars developed strange ideas like
1 -Trinity
2 -Jesus is God in flesh
3 -Jesus is 'crucified' for the sins of others.
which even some christians object and are different from all monotheistic religions.
Why are bible and torah corrupted ,when it was a revelation from God ?
Because they were not the last revelation.
Because Jesus(pbuh) and Moses (pbuh) were not the last messengers.
Lets make something clear.
We muslims have to believe all the prophets and books which
are sent by Allah to be a muslim.Quran and islam is the last revelation from Allah. The corruption of other holy books are allowed by Allah but Quran will be preserved till the end of the world .It is assured in Quran.
Quran is a miracle by itself. We see clearly how Quran will be preserved.
Quran is memorised by 8 million people in the world today .
Even if all copies of Quran are destroyed , Quran can be written
error free again .This is the proof of the preservation.
The memorising is going on since the first days of the revelation of Quran.
Only this is a miracle by itself,besides mathematical , scientific miracles of the Quran , which are known day by day.