Islam is a Deen – religion. Deen means a complete system of life consisting of beliefs and laws. To know the Islamic attitude towards the laws of the shari’ah, we have to study the Qur’an and Hadith. In the Qur’an and hadith, we find two different attitudes towards two different aspects of deen.
“Why do we have to pray five times a day?” “Why are dogs and hogs regarded unclean (najis)?” “Why is an animal slaughtered in a non-Islamic way forbidden (haram) and unclean?” These are but a few of the many questions asked by our youngsters about the laws of the Shari’ah. They want to “rationalize” each and every law of the shari’ah; they want to know the reason and purpose of the legislation of these laws. Before explaining the validity or otherwise of the “rationalization” of the shari’ah, it seems necessary to clarify the fundamental attitude of a Muslim towards the shari’ah.
Islam is a Deen – religion. Deen means a complete system of life consisting of beliefs and laws. To know the Islamic attitude towards the laws of the shari’ah, we have to study the Qur’an and Hadith. In the Qur’an and hadith, we find two different attitudes towards two different aspects of deen. These two aspects of deen are: a) the fundamental beliefs known as Usul ud-Deen, the roots of religion; b) the laws of the shari’ah, known in general as Furu ud-Deen, the branches of religion.
In regard to the “roots of religion”, Islam expects Muslims to hold our belief in the fundamentals of our religion after attaining conviction of their truth through examination and reflection. The Qur’an clearly condemns those who follow others blindly in matters of beliefs: “There is no compulsion in [accepting the] religion [of Islam because] truly the Right Way has become clearly distinct from error.” (2:256) Again, the Qur’an says: “And when it is said to them, ‘Come to what Allah has sent down, and the Messenger,’ they say, ‘Enough for us is what we found our fathers doing.’ What, even if their fathers had knowledge of naught and were not rightly-guided?” (5:104) This strong condemnation of the idol-worshippers is repeated elsewhere: “And when it is said to them, ‘Follow what Allah has sent down,’ they say, ‘No, but we will follow such things as we found our fathers doing.'” (2:170 and 31:20) Islam says that one may consider the views and opinions of others, but that one should only accept that which is reasonable to believe: “So give (O Muhammad) good tidings to My servants who give ear to the word and follow the fairest of it. Those are they whom Allah has guided, and those are men possessed of minds.” (39:17)
Likewise, in the books of narrations, we find the Prophet and the Imams of Ahlul Bayt (peace be upon them) using intellectual arguments in matters of beliefs to convince their opponents or the seekers of truth. This itself is an example and Sunnah for the Muslims to base our beliefs on understanding and conviction. But when it comes to the “branches of religion”, Islam expects absolute obedience from Muslims. The reason of this expectation is very obvious: once a Muslim has believed, by his own free will, in Allah as the Creator and the Wise Author of laws, in Muhammad as the infallible Messenger of Allah, and in the Qur’an as the message of Allah, it follows as a necessary consequence that he must adhere to the shari’ah. This absolute obedience regarding the shari’ah can be inferred from the following verses:
“It behooves not a believing man and believing woman that they should have any choice in their affairs when Allah and His Messenger have decided a matter; and whosoever disobeys Allah and His Messenger, he surely has strayed off a manifest straying.” (33:36)
“O you who believe! Do not take precedence before Allah and His Messenger [in matters of the shari’ah] and fear Allah; surely Allah is Hearing, Knowing.” (49:1)
“O you who believe! Obey Allah, obey the Messenger, and those who are in authority among you (i.e., the Imams).” (4:59)
“We have not sent a Messenger but to be obeyed.” (4:64)
To summarize: In Islamic beliefs, a Muslim is expected to believe only after reflection; and in Islamic laws, he is expected to follow them without any reservations.
Now, we come to the problem that why such and such law of the shari’ah was legislated. Considering the reasons and purposes of the laws, the shari’ah can be divided into four categories:
The First Category
The laws whose reasons and purposes are self-evident, like helping the needy is highly recommended, killing is forbidden, paying taxes like khums and zakat is obligatory. One does not need any expertise or extraordinary intelligence to know that helping the needy is good, paying taxes is necessary for preserving the financial equilibrium in the society, and killing and lying is evil.
The Second Category
The laws whose reasons and purposes have been explained in the Qur’an and hadith, like intoxicants are forbidden, interest is prohibited, fasting in the month of Ramadan is obligatory, and prayers is obligatory.
The Qur’an and the hadith have said that intoxicants are among the main causes of evil, because an intoxicated person is no longer in control of himself. Although it took the world a long time and a bitter experience to realize the harm of drunkenness, Islam declared its harm and evil 1400 years before by saying that “its sin is greater than its [financial or other] profit.” (2:219)
Interest is prohibited. The Qur’an and hadith have explained the harm of interest. Interest leads to destruction of the poor section of the society, and all wealth gravitates towards the already wealthy group. 
Fasting is a physical and spiritual training which brings the servants of Allah nearer to Him and makes them more obedient to the shari’ah.
Prayer is a means of expressing our gratitude to Allah. “O you who believe! Eat of the good things that We have provided you with and thank Allah.” (2:172) It is an important way of achieving peace of mind. “Surely by Allah’s remembrance are the hearts set at rest” (13:28). And it is also a very effective method of making the believer more obedient to the laws of Allah. “Surely prayer keeps (one) away from indecency and evil.” (29:45)
There are many traditions of our Imams explaining the reasons and purposes of many laws of the shari’ah. Shaikh as-Saduq has collected many of these narrations in his ‘Ilal ash-Sharaya.
The Third Category
The laws whose reasons and purposes have not been explained in the Qur’an or hadith, but the rising horizons of human knowledge have helped in understanding their purpose and usefulness, for example, why the meat of hog is forbidden, why circumcision is highly recommended by the shari’ah, and why only the fish which has scales is permitted in Islam. 
For the benefit of circumcision, we quote Sherman Silber who says that: “There are a number of reasons why circumcision is beneficial and why it ought to be performed in infancy. First, it prevents cancer of the penis in later life. Cancer of penis generally occurs when there has been carelessness in taking care of one’s foreskin. A second benefit of circumcision is that the wives of circumcised men are less commonly afflicted with cancer of the cervix. The most common benefit of circumcision is that it prevents accumulation of oils and secretions (called smegma) under the foreskin, which lead to infection, swelling, and sometimes contraction of the foreskin so the tip of the penis is trapped inside.” 
About the fish, it has been said that the fishes that do not have scales are harmful to human beings. Based on that research, American troops in the east were directed that “tropical marine fishes without scales were to be left alone.”
It must be mentioned here that the reasons of the shari’ah laws which have been discovered by human knowledge cannot be regarded as the actual reason (ratio legis) for the legislation of those laws, because the human knowledge is still in its infancy whereas Islam, the final shari’ah of Allah, is to stay in practice up to the end of this world. However, the scientific facts can be used to explain the usefulness and benefits of the laws of the shari’ah.
The Fourth Category
The laws whose reasons and purposes have neither been explained in the Qur’an and hadith, nor the new advancement in human knowledge has been able to explain them. For example, why four units in Dhohr, Asr, and Isha prayers, while only three in Maghrib, and two in Fajr?
As far as the first three types of laws are concerned, there is not much problem in explaining their reasons and purposes. The problem arises when one starts to rationalize the laws which come under the fourth category.
Regarding the laws of the fourth category, the only thing which can be said is that a Muslim should have complete faith that there surely are useful purposes in these types of laws. The purposes can be of material or spiritual nature, or both. Why we should have such a confidence in these laws of the shari’ah? Because we, the Shia Ithna Asharis, believe that all the actions of Allah have purpose, and that they are for the benefit of human beings; and this includes the laws of the shari’ah.  On basis of this belief, we must have confidence that all His laws (including the ones whose purposes are still unknown to us) have a purpose and benefit for human beings.
One more thing which must be clarified at this point is that it is not the responsibility of the scholars to discover and explain the purpose and reason underlying the laws of the shari’ah. Their only duty is to explain the laws of the shari’ah. The people responsible for discovering and explaining the purposes of the laws of the shari’ah are those Muslim intellectuals who are experts of modern science. Unfortunately, very few of them are interested in this aspect of the shari’ah, and those who are interested lack the knowledge of Qur’an and hadith.
The belief that although we might not know the reason and purpose of a certain law of the shari’ah it surely has a good reason and useful purpose behind it can be understood from the following episode in the Qur’an. This episode also shows that if we are made aware of its reason, we would readily admit that it was the very right thing to do.
One day while preaching to his people, Prophet Musa (peace be upon him) thought that Allah has given him a great privilege and that he is the most learned among mankind. Allah was not pleased with even such a slight indication of pride in the mind of Musa, and so Jibrail was sent to inform Musa that there is a person among the servants of Allah who is more learned than him. He was also given an address to go and meet this more learned person. Musa, along with one of his disciples, went to meet the learned person who is named in our narrations as Khidr. The Qur’an narrates the details of their meeting:
Musa: Can I follow you so that you may teach me the right knowledge of what you have been taught [by Allah]?
Khidr: Surely you cannot have patience with me. How can you have patience in [the things or actions] of which you do not have a comprehensive knowledge?
Musa: If Allah wills, you will find me patient, and I shall not disobey you in any matter.
Khidr: If you would follow me, then do not question me about anything until I myself speak to you about it.
So they went their way until they reached a river where they embarked in a boat. When they were in the boat, Khidr made a hole in it.
Musa: Have you made a hole in it to drown its inmates? Surely you have done a grievous thing!
Khidr: Did I not say that you will not be able to have patience with me?
Musa: O Khidr, do not blame me for what I forgot, and do not constrain me to a difficult thing in my affair.
Then they went on until they met a boy. Khidr slew that boy.
Musa: Have you killed an innocent person who had not killed someone else?! Certainly you have done an evil thing.
Khidr: Didn’t I say to you that you will not be able to have patience with me.
Musa: If I ask you about anything after this, then do not keep me in your company; indeed, you shall then have found an excuse in my case [to dismiss me from your company].
They went on until they came to a township. They asked food from the people of that town, but no one accepted them as guests. In that town they found a wall which was on the point of falling in ruin, so Khidr repaired the wall and put it into the right state.
Musa: If you had wished, you might certainly have taken a payment for this work.
Khidr: This shall be the parting between you and me. But before you leave, I will inform you of the significance of my actions which you could not understand:
– As for the boat, it belonged to some poor men who worked on the river. I wished to damage the boat because a king was coming behind them who seized every good boat by force.
– As for the boy, his parents were believers, and I feared lest he would oppress them by rebellion and disbelief. And we desired that their Lord might give then in his place a better one than him in purity and nearer to having compassion.
– As for the wall, it belonged to two orphan boys in the city, and there was beneath it a treasure belonging to them, and their father was a righteous man; so I rebuilt the wall because your Lord desired that when they attain maturity, they should take out their treasure, which was a mercy from your Lord.
And moreover, I did not do it of my accord. This is the significance of that with which you could not have patience. (18:60-82)
If such a great prophet of Allah like Musa could not understand the significance of the actions of a fellow human being who was more learned than him, then how can we expect to know the wisdom and purpose of each and every law which has been legislated by Allah, the Wise, the Omniscient and the Omnipotent?!
 For a detailed discussion on interest, see Allama Tabatabai’s al-Mizan (translated by S.S.A. Rizvi), vol. i, Wofis, Tehran 1982, pp. 295-303.
 For a detail discussion on pork, see Pork by S.S. A. Rizvi, published by Wofis, P.O. Box 2245, Tehran.
 Sherman Silber, The Male. New York, 1981, pp. 115-116.
 Allama Hilli, al-Babu ‘l-Hadi ‘Ashar, (translated by W.M. Miller), Luzac, London 1958, pp. 45-46.