As the Quran itself attests, it is a universal book “a reminder to all worlds” for all people in all times and places “a warner to all mankind”.
Its verses, which have been revealed by Allah, are and will be an answer to the guidance needs of mankind till the end of time, and will blaze as their torch of guidance, benefiting them with its valuable teachings.
Since the Prophet of Islam is Allah's final messenger and Islam is His last religion and as a result neither the Prophet will be followed by another prophet, nor Islam will be followed by another religion, one can conclude that the Holy Quran must be a complete book that is to be eternal and for all mankind in all ages to come (or else Allah wouldn't stop sending prophets with new religions and would provide them with new religions).
The history of the Quran and its tafsir, both show that as a result of its blessed being, open-minded individuals have been able to learn new things from it in different eras and that it has been able to meet both the old and modern needs of mankind and answer all of its questions. Of course, such a matter has been accomplished by: 1- The Quran giving us general rules, principles and guidelines on guidance. 2- Our scholars finding the instances of these principles, where each is supposed to be applied and reaching more specific rulings using ijtihad (Islamic jurisprudence).
As for what has been claimed in the question above, that the Quran's verses contradict and correct one another, isn't true. We believe that no verse in the Quran contradicts the other and that paradox or falsehood have no way in it. Maybe what is meant is that some examples of "naskh" (abrogation of decrees) can be found in the Quran, but one should note that the abrogation of some decrees doesn't mean that the verse expressing the new decree is contradicting or correcting the previous. That is because naskh means for a temporary decree's time to run out and for a new one to take its place, not for a permanent decree to be corrected by a new one. Therefore, if at the first glance sometimes it might seem as if there are some contradictions in the Quran, one must be aware that these are only at the first glance, and that since the Quran's verses explain one another and confirm each other, its commentators have solved these so-called contradictions and explained what is exactly meant by these verses.
As the Holy Quran itself attests, it is a universal and eternal book consisting of the answer to man's needs in all times and space, and doesn’t exclusively belong to a certain race or tradition. “a reminder to all worlds”, “a warner to all mankind”
Allah (swt) has put the Quran together in a way so that all people in every era throughout history can make good use of its pure teachings. The Quran's history and tafsir also show that because of its blessed existance, open-minded individuals have been able to learn new things from it during the course of history, and that the fruit of its teachings has answered the needs of mankind and has quenched its thirst for godly teachings.
There are many different ways one can use to prove that the Quran is a complete, ever-lasting and universal book for all people. Some are mentioned below:
1) In the Quran, there are verses that say that Islam has been completed and that all of the laws and rulings that needed to be legislated, have been legislated and that there is nothing else left to say. Verses like: “We have not neglected anything in The Book” and “Today I have perfected your religion for you, and have completed My blessing upon you” and other similar verses.
2) Imam Sadiq (as) was asked about the newness and freshness of Quranic teachings; his Excellency responded: “The reason behind why the Quran remains fresh is that Allah (swt) hasn't revealed the Quran for a certain time or people, and since it is perpetual and for all, it will be new in all eras and will remain sweet and interesting for all people till the day of judgment.”
3) Since the Quran is Allah's final book, it must be a complete one, capable of fulfilling all of man's needs concerning guidance, because the whole purpose of sending messengers is to guide mankind through revelation and to lead them to their eternal bliss and prosperity and spirituality by teaching them true beliefs and the right actions or the dos and don’ts of religion. Since man’s life is always going through change and is continuously developing and he is in need of a religion that can answer to all his guidance needs, Islam and Prophet Muhammad need to have a special quality making them differ from other religions and allowing them to be the final religion and messenger of God respectively so that there is no need for a new religion or messenger afterwards.
In other words, in order for the Quran to be continuous and for all to be able to refer to, it must never get old and out-of-date and must remain fresh and up-to-date. Moreover, the Quran isn't simply a book that solely speaks of Islamic beliefs and decrees, the history of past nations, the eternal bliss of the world to come and how to reach high levels of spiritual perfection, but it also directs us to special guides who can show us the path and help us along the way. They are the leaders of religion and those firmly grounded in knowledge (rasikhoon fil-ilm) who are able to find the true interpretation of mutashabih verses (metaphorical verses who need to be explained and interpreted in order to reach the true meaning of the verse) using muhkam (definitive and decisive verses whose meanings are obvious) ones and find the rulings of new and modern issues by establishing the method of ijtihad (jurisprudence). The Quran has prescribed the referring of the laity to the experts or the rasikhoon fil-ilm during the era of Islam’s being the final religion, and has also urged them to lead the Muslim nation using a general plan, and deriving, explaining and interpreting specific doctrines that fit their time and conditions. This is the role that the rasikhoon play. Therefore, it is the responsibility of these scholars to apply general rules and principles and interpret different rulings, and make use of the eternal sources of revelation, while taking into consideration all of the different aspects of the time and conditions they live in and the new issues that come up. Sometimes, an issue that had never come up in the society at the advent of Islam, comes up in today’s society and is considered a necessity. New needs are answered to by today’s scholars applying principles to specific issues. In reality, this is exactly what being “the final religion” means and that is what the Quran means when it says that it is “a clarifier and explanation of all things” (meaning that it has given us general principles and guidelines that we can use to see what our duties are, not that it has explained every single detail in the universe in a detailed manner).
After this relatively long introduction, let’s get back to the main question:
We believe that on the outside, the Quran is of a beautiful form (eloquence) and on the inside, it is of harmony between all of its different sections, such that no contradiction can be found in its verses and its various rulings. None of its verses contradict one another, on the contrary, they are always confirming one another and no falsehood nor paradox can be found in its verses.
“Do they not contemplate the Qur'an? Had it been from (someone) other than Allah, they would have surely found much discrepancy in it”
But if “abrogation of decrees” or “naskh” is what you mean by the contradiction between the verses of the Quran, one must say that naskh literally means to get rid of something and replace it with something else, and in Islamic terms, means for an Islamic rule to be nullified as a result of its time limit ending.
Three types of naskh can be pictured regarding the Quran:
1- The naskh or abrogation of Hukm (ruling) and Tilawah (recitation): This means for a verse of the Quran containing a ruling to be omitted. As a result, neither the verse no longer exists, nor does the ruling in which it was disclosing before being omitted. Since this type of naskh is a form of falsification, one can be sure that this type of naskh will never occur in the Quran and isn’t possible.
2- The naskh of Tilawah only: this means for a verse containing an Islamic ruling to be removed, without its ruling being touched. In other words, the verse is no longer in the Quran, although its ruling remains in Islamic law. For some particular reasons that we won’t take time in mentioning, this form of naskh is also unacceptable and isn’t possible.
3- The naskh of Hukm only: this means for a verse containing a certain ruling to remain, while its ruling no longer existing. This third type is both possible and has taken place in the Quran and all commentators have accepted it. What must be noted is that this type of naskh, is neither considered self-contradiction in speech, nor a change of mind, what it truly is, is a change in ruling as a result of different situations and a change in instances. In other words, sometimes an act might have certain benefits and advantages, causing it to have a certain ruling, and as soon as these advantages cease to exist because of certain changes in conditions and situations, the ruling also changes, meaning that unlike normal and usual cases of rulings, the ruling of that act was limited from the beginning; limited to the advantages it had, not that its ruling was to be forever no matter what the conditions.
Some Quranic verses, like verse 101 of surah Naml, and verses 106 and 107 of surah Baqarah, express such a matter.
Of course, there are reasons behind naskh in the Quran; the main goal that the Quran was revealed for is the development of human society. Human society is like a patient in need of a curing prescription. Clearly, in order for the patient to get better, after using a medicine for a prescribed amount of time and the medicine having its effects, another medicine needs to be prescribed. This doesn’t mean that the first medicine was wrong in the first place, it means that in order for the job to get done, the first medicine needed to be taken for a specific period and then continued by another one. The Quran is the curing medicine for those who suffer from spiritual illnesses such as: ignorance, arrogance, selfishness etc. and have no clue of spiritual truths and high virtues. In order to save these “patients”, a precise program is necessary to slowly, yet steadily purify them of bad characteristics and replace them with good ones. Naskh is a very natural and ordinary subject when it comes to low societies trying to slowly perfect and purify themselves. In many cases, sudden change and transference can be dangerous and of negative effect, while methods that work step by step are more affective. This doesn’t mean that Islam doesn’t have the quick solution, it means that sometimes the “patient” doesn’t have the needed capacity for a sudden change. Therefore, naskh is somewhat like a temporary treatment that has the needed effects for the treatments to come.
So, two verses or rulings (one being the nullifier or nasikh of the other, while the other being the nullified or mansookh) might sometimes seem to contradict one another, although they truly don’t, because each have their own advantage and reason, the only thing is that the benefit and reason of the first one ends causing the next one to begin.
The same goes for the muhkam and mutashabih verses of the Quran. As the Quran itself attests, it contains both mutashabih and muhkam verses. One reason for why the Quran contains mutashabih verses can be that not all people are smart and intelligent, at the same time metaphysical concepts are hard to comprehend while words sometimes cannot bear these high and complicated concepts and express them because language has been invented to be used for everyday things.
Divine messengers have been sent to all people, and naturally, all types of individuals can be found in them; smart, intelligent, normal and unintelligent and sometimes even dumb, while many deep and complicated concepts have been mentioned in a way that othrer than a few of the elite, not all can comprehend. Such knowledge and comprehension is possessed by rasikhoon fil-ilm.
Conclusion: Such contradictions in no way mean that there is any form of paradox or transformation in the Quran, so that as a result it can no longer be a book of guidance for all of mankind.
 The Holy Quran, An'am:90.
 Ibid, Muddathir:36.
 For further information, see: Question 135.
 The Holy Quran, An'am:37.
 Ibid, Ma'idah:3.
 Biharul-Anwar, v.89, pg.15, Noorul-Thaqalain, v.3, pg. 740.
 Seyyid Ali Ayazi, Jame’iyyate Quran, pg. 51. (For further information on the Quran and Islam being the final ones of their type, see: Morteza Motahhari, Khatamiyyat, Jafar Subhani, Khatamiyyat az Nazare Quran va Hadis, Muhammad Taqi Mesbah Yazdi, Rahnama Shenasi.)
 Fussilat:41-42. (No falsehood finds way to it neither from the front nor from behind; a (gradually) sent down (revelation) by the all-wise, all-laudable)
 Seyyid Ali Akbar Quraishi, Qamuse Quran, vol.7, the term naskh.
 Seyyid Abul-Qasem Khu’i, Al-Bayan, pg. 277-278.
 Ibid, Nisa:82.
 “For any verse that We abrogate or remove from memories, We bring another which is better than it, or similar to it…” Baqarah:106. See: Fakhr Razi, Al-Tafsirul-Kabir, vol. 3 and 4, pg. 226, Tafsir Nemouneh, vol. 11, pg. 405, vol. 1, pg. 388. Some verses that have gone through naskh are as follows: verses 15 and 16 of surah Nisa’ which has been nullified by verse 2 of surah Nur, verse 12 of surah Mujadilah that speaks of giving charity before having a private talk with the Prophet (pbuh) which has been nullified by verse 13 of the same surah.
 Mahdi Ahmadi, Quran dar Quran, pg. 103-112.
 The Holy Quran, Alu-Imran:7, Nisa:162.