The reason for the differences between the rulings of the Torah and of the Qur’aan
Question

A central belief of both Islam and Judaism is the belief in one God and the prohibition of the worship of idols.
The main difference between these two purely monotheistic religions is the book of each religion, the Koran and the Torah. How do the teachings of the Koran differ from the teachings of the Torah.
Praise be to Allah.Firstly: 
We welcome you to our website and we ask Allah to help us to present useful information to you, and that this will be beneficial to you in both spiritual and worldly terms. 
Secondly: 
If you are speaking about the Judaism that was prescribed by God and the Torah that God revealed, then Islam and Judaism are agreed – as you said – on the worship of God alone, with no partner or associate, and on the prohibition of worshipping anything or anyone else, no matter what it is. Similarly, they are agreed on matters of belief in the Prophets and Messengers, the Last Day, the Reckoning, Paradise, Hell… and so on. 
But when it comes to rulings such as what is permissible and what is prohibited, and the details of acts of worship, this is where Islam differs from Judaism and the Qur’an differs from the Torah. God, may He be exalted, says in the Holy Qur’an (interpretation of the meaning): “To each among you, We have prescribed a law and a clear way”[al-Maa’idah 5:48]. So each nation has its own laws concerning what is permitted and what is forbidden, as it has its own acts of worship by which it worships Allah. 
Our Prophet (blessings and peace of Allah be upon him) gave the likeness of the agreement of all the Prophets on the basic matter of religion, which is affirmation of the Oneness of God (Tawheed), beliefs and worship of God alone, with no partner or associate, and the differences between their laws, when he said: “The Prophets are half-brothers; their mothers differ but their religion is one.” Narrated by al-Bukhaari and Muslim. 
Half-brothers refers to brothers from the same father, with different mothers. 
So the basis of the religion of the Prophets is one, namely affirmation of the Oneness of God (Tawheed), and worshipping God with no partner or associate, but the details of laws and rulings is what is different. 
And this is what is in accordance with wisdom. 
Adam (peace be upon him) had a law that was suited to him and his children, and was suited to the time in which he lived. In his law – for example – a brother could marry his sister, because it was not possible to perpetuate the family and produce offspring at that time in any other way. 
Then as time passed, the laws changed to suit the new nations and new times. Hence in the laws of the Jews it is forbidden for a brother to marry his sister, even though that was permitted in the law of Adam. 
For Jacob (peace be upon him), all kinds of food were permissible and he was the one who forbade some things to himself, and those prohibitions became entrenched and became a law for him and his children. Concerning that God, may He be exalted, says in the Holy Qur’aan (interpretation of the meaning): “All food was lawful to the Children of Israel, except what Israel made unlawful for himself before the Taurat (Torah) was revealed” [Aal ‘Imraan 3:93].  
Then came the law of Jesus (peace be upon him), which was more lenient than the law of Moses. God permitted to the Christians (the followers of the Messiah, peace be upon him) some things that had been forbidden in the law of Moses. Concerning this God, may He be exalted, tells us that Jesus (peace be upon him) said (interpretation of the meaning): “and to make lawful to you part of what was forbidden to you” [Aal ‘Imraan 3:50]. 
Then came the law of the Qur’aan, the law of Muhammad (blessings and peace of Allah be upon him) which also differed from previous laws in some rulings, as had happened before that in the case of Judaism and Christianity. 
Because the law of the Qur’aan is the final law that will abide until the Day of Resurrection, it is the most complete of laws, the best and the most lenient, and in it is flexibility that is suited to all times and places until the Hour begins. 
This is the reason for the differences between the rulings of the Torah and the rulings of the Qur’aan, as the Torah was specifically for the Children of Israel alone, and its rulings were not meant to be permanent and ongoing until the Day of Resurrection. Although most of the rulings of the Torah remained in effect after that in Christianity, and only differed in making permissible some things that had been forbidden, the rulings of the Torah, and the Gospel after it, were limited in terms of time and all of that came to an end at the appointed time, which was the coming of the Prophet Muhammad (blessings and peace of Allah be upon him). A covenant had been taken from the Prophets who came before him that if he was sent when any of them were still alive, they would abandon whatever they had and follow him. God, may He be exalted, says (interpretation of the meaning):
“And (remember) when Allah took the Covenant of the Prophets, saying: ‘Take whatever I gave you from the Book and Hikmah (understanding of the Laws of Allah, etc.), and afterwards there will come to you a Messenger (Muhammad (blessings and peace of Allah be upon him)) confirming what is with you; you must, then, believe in him and help him.’ Allah said: ‘Do you agree (to it) and will you take up My Covenant (which I conclude with you)?’ They said: ‘We agree.’ He said: ‘Then bear witness; and I am with you among the witnesses (for this).’
Then whoever turns away after this, they are the Fasiqoon (rebellious: those who turn away from Allah’s Obedience).”
[Aal ‘Imraan 3:81-82]. 
The law of the Qur’aan differs from all the laws that came before it in that it is suitable for all kinds of people at all times until the end of this world. 
But if you were talking about the Torah as it exists now, then we have no choice but to tell you of what we really believe – even if that may upset you – but we hope that you have strong reason and sound thinking that will help you to distinguish between truth and falsehood, and that this may motivate you to investigate further until you reach the truth. 
This truth is that the Torah as it exists today is not that which God sent down to Moses (peace be upon him). Rather it has been distorted in all ways, adding, subtracting and changing the meaning. This is not the place to expand upon this topic; we are just referring to it in the hope that this might motivate you to enquire further. 
The Torah as it exists today contains material that one must be certain is not the words of God; rather it is distortions introduced by those who attributed it falsely to God, may He be exalted. 
For example: 
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It contains the ascription of shortcomings to the Lord, may He be glorified and exalted, and likens Him to created beings. For example, they say that God wrestled with Jacob for an entire night, then Jacob overpowered Him! And they say that God regretted having created mankind when He saw their disobedience, and He wept until His eyes became swollen, then the angels came to visit Him and comfort Him. Exalted be God far above what the wrongdoers say. 
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It contains insults and slander against the Prophets. For example, they say that the Prophet of God Aaron made a calf and worshipped it along with the Children of Israel. And they say that Lot drank wine until he became drunk, then he committed incest with his two daughters, one after the other! And they say that Solomon (peace be upon him) apostatised at the end of his life and worshipped idols, and built temples for them. 
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It includes exaggerations, impossible things and contradictions. 
Among the books that have been written on this topic are “What is the Origin of Man?” and “The Bible, the Qur’aan and Science” by the French scientist and medical doctor Maurice Bucaille, in which he proved the existence of scientific errors in the Torah and Gospel, and at the same time he proved that there are no contradictions in the Qur’aan even with modern science and scientific facts. 
He says in the introduction to his second book (p. 29): 
“It was in a totally objective spirit, and without any preconceived ideas that I first examined the Qur’anic Revelation. I was looking for the degree of compatibility between the Qur’anic text and the data of modern science. I knew from translations that the Qur’an often made allusion to all sorts of natural phenomena, but I had only a summary knowledge of it. It was only when I examined the text very closely in Arabic that I kept a list of them at the end of which I had to acknowledge the evidence in front of me: the Qur’an did not contain a single statement that was assailable from a modern scientific point of view.
I repeated the same test for the Old Testament and the Gospels, always preserving the same objective outlook. In the former I did not even have to go beyond the first book, Genesis, to find statements totally out of keeping with the cast-iron facts of modern science.” 
Based on that, we have two reasons why the Torah as it exists now differs from the Qur’aan: 
1.Differences in the laws of the Prophets
2.Distortion that crept into the Torah and the tampering that happened to it with the passage of time.
We ask God to show us the truth as truth and enable us to follow it, and to show us falsehood as false and enable us to avoid it. 
And Allah knows best.