Thus, first, in reality, human nature actually does not change over time. Laws or guidance covering moral and ethical behavior shall always remain the same, because what is damaging to the soul at one time will always be damaging to the soul, again due to the fact that human nature does not change. For example, lying and cheating are displeasing to the Lord and harmful to the soul and shall forever remain that way. Thus, laws and guidance related to issues of this nature remain fixed and completely applicable until the Day of Judgment. Ritual acts of worship, which underline the foundation of a human's character, also do not need to change. God alone knows how He is to be worshipped, and if He has declared these acts as proper and acceptable to Him until the Day of Judgment, no one can possibly say otherwise. In describing these kinds of laws or guidance, one can say that Islamic Law is rigid, but that is only because it should be rigid on these points. That, in no way, affects its universality and practicality for all times and places.
Second, there are some harmful matters that humans must avoid. These have also been explicitly and permanently forbidden. Alcohol and intoxicants, for example, will always be harmful for humankind. Every now and then, humans may find something beneficial about alcohol, as God also alludes to in the Quran, but overall no society can rightly argue that alcohol consumption is something good. One need only consider the social costs of drinking in the United States alone. Many families are torn apart due to alcohol abuse. Driving under the influence is recognized as a danger to society, and although great steps have been taken to control it, numerous people are still killed or severely injured due to alcohol. Many alcoholics cannot hold down jobs and thus become dependent on the state, putting the burden of their care on the rest of the citizens. When it comes to issues of this nature, Islam forbids such a practice forever as there can be no serious argument given that alcohol should be permitted. (Indeed, one can argue that it is only permitted today because the cost of keeping people from this addicting “drug” is prohibitive. This, in reality, is just another sign of how dangerous and evil alcohol is.)
Third, beyond that, humans need only some detailed laws but many general principles that allow them to guide their lives in all times and places. This is exactly what Islamic Law provides for them. Thus, God provides detailed laws about what kinds of food one may eat, inheritance, who is legal as a spouse, international relations and so on. From these detailed laws, a scholar is able to extract rulings for many new occasions. From the general principles, a scholar can derive guidance for various issues that did not occur during, for example, the time of the Prophet.
Fourth, in the realm of social contracts and business, for example, the general principle is that everything is permissible unless there is evidence to show otherwise. Hence, Islamic Law actually allows for a great deal of freedom within the Law. In business dealings, for example, Islam has prohibited interest, overly risky transactions, gambling, fraud, deception, sale or purchase of illegal items and coercion. In general, these are the harmful aspects that have been prohibited. In other words, the guidance is such that when new forms of business dealings are developed, as in modern times, one can determine which are acceptable according to Islamic guidelines and which are not. Thus, Islamic Law has been proven to be feasible for over 1400 years and, according to Islamic beliefs, will continue to be feasible until the Day of Judgment. Two businessmen are able to come up with any form of contract they wish, as long as the basic forbidden and harmful aspects are avoided. One cannot even imagine how many types of transactions are therefore permissible under Islamic Law.
Finally, it must be recognized that this complete and comprehensive guidance that will remain viable until the Day of Judgment is a great blessing from God, and is another sign that humans must turn to God for guidance. Humans on their own would never be able to find a way of life that is suitable even for just one place and time, not to speak of something that would be good for centuries or millenniums—although humans would try to latch on to what they were following in the past. Sayyid Qutb has eloquently noted this point when he wrote,
When a human being tries to construct a metaphysical concept or a system of life through his own efforts, this concept or system cannot be comprehensive. It can only be partially valid, good for one time and place but not for other times and other places, and appropriate for one set of circumstances but not for another. Furthermore, even in tackling a single problem, he is incapable of looking at it from all possible sides and of taking into consideration all the consequences of the proposed solution, since very problem extends in space and time and is connected with precedents and antecedents beyond the scope of observation and comprehension of human beings.
We therefore conclude that no philosophy and no system of life produced by human thought can have the characteristic of “comprehensiveness.” At most, it can cover a segment of human life and can be valid for a temporary period. Because of its limited scope, it is always deficient in many respects, and because of its temporariness it is bound to cause problems that require modifications and changes in the original philosophy or system of life. Peoples and nations basing their social, political and economic systems on human philosophies are forever confronted with contradictions and “dialectics.”
One need only look at one example which has been much debated recently to understand how applying God’s guidance at all places and times is what is best for humanity. Circumcision is a well-known and established practice in Islam. In the past few decades, doctors and scientists—due to humans’ very limited understanding of the reality of humans as a whole—keep going back and forth concerning circumcision. One decade they are in favor of it while the next they say that it is useless and harmful to the child. Now they have found—or they think they have found, as perhaps they could be wrong again—that circumcision is a great defense against HIV AIDS. Now, they are rushing to circumcise many of the men in different parts of Africa.
Perhaps, after so many cases like this, more and more humans will realize that there is guidance, complete and perfect, that has come from God that is exactly what all humans need and require, regardless of time and place.
The Guidance is Complete and Sufficient Forever
In sum, the guidance is complete and suitable for all times and places. It is all that the Muslims need for happiness in this world and in the Hereafter. It cannot be improved upon. It is, therefore, in no need of additions, alterations or deletions. Those who think that they can improve upon what God has revealed are arrogant in the purest sense and going beyond what they can possible ever achieve. For this obvious reason, the Prophet gave very strong warnings about innovations, heresies and changes to the faith. Such things are not needed at all and they will simply take away from the beauty and perfection of Islam. Thus, the Prophet said:
“The worst matters are invented ones. And every innovation is a going astray.” (Saheeh Muslim)
He also said:
“And every going astray is in the hell fire.” (al-Nasaai)
The Prophet also said:
“Whoever introduces anything into this affair of ours that does not belong to it will have it rejected.” (Saheeh al-Bukhari and Saheeh Muslim)
 Sayyid Qutb, The Islamic Concept and Its Characteristics (American Trust Publications, 1991), pp. 85-86.