Every Muslim agrees on the fact that the Holy Qur'an came down as a revelation to the Prophet Muhammad (PBUH&HP)  in Arabic as we see in the following two verses:

The Holy Quran 43:3  
"Surely We have made it an Arabic Qu'ran that you may understand."

The Holy Quran  12:2
"Surely We have revealed it-an Arabic Qu'ran-that you may understand."

Do I need to read the Holy Quran in Arabic or can I just read it in English?

Today with uncountable nationalities embracing the fold of Islam, many read the Holy Qu'ran in their native tongue and thereby pose different questions and arguments about reciting it in their own tongue.  

These arguments include the following:

1. It is not wajib (Obligatory) to read the Holy Quran in Arabic because it is not specifically mentioned in the Holy Qu'ran that we must read it in Arabic.

2. Non-Arab Muslims do not understand the Holy Quran in it's revealed language and since Islam is a way of life, then it is more important to understand the injunctions, clear signs, stories of the Holy Prophets (AS) of Allah to gain guidance from these instead of spending time; learning a language, reciting in that language that they believe does not benefit them and that the time in which they would be occupied in reciting a language that is, they feel, not of use to them, then this time although not exactly wasted can be put to better use in acquiring actual knowledge.  

Some argue that they can not learn  Arabic because they are not good with languages and others still insist that while they read the Holy Quranic interpretations in their native language in the holy month of Ramadan, they have actually completed an entire Quran that month. 

And a final argument given is the following:

"I do not understand at all why the Quran should be read in Arabic? Yes, Allah Almighty has said that we sent the Qur'an in Arabic for you to think about, but if we read the Qur'an in Persian, can we not think about it?"
So let's begin to answer these arguments by going directly to the Holy Qu'ran where the word Arabic is mentioned exactly ten times and see what Allah is telling us.

In the Holy Quran 12:2,
"Surely We have revealed it-an Arabic Quran-that you may understand."

In the Holy Quran 13:37,
And thus have We revealed it, a true judgment in Arabic, and if you follow their low desires after what has come to you of knowledge, you shall not have against Allah any guardian or a protector. 

In the Holy Quran 16:103,
And certainly, We know that they say: Only a  mortal teaches him.  The tongue of him whom they reproach is barbarous, and this is a clear Arabic tongue.

In the Holy Quran 19:97,
So We have only made it easy in your tongue that you may give good news thereby to those who guard (against evil) and warn thereby a vehemently contentious people.

In the Holy Quran 20: 113,
And thus have We sent it down an Arabic Quran, and have distinctively set forth therein of threats that they may guard (against evil) or that it may produce a reminder for them.

The Holy Quran 26:193,194,195 and 200
193. The Faithful Spirit has descended with it.
194. Upon your heart that you may be of the warners.
195. In plain Arabic language.
200. Thus have we made it enter into the hearts of the guilty.

The Holy Quran 39:28,
An Arabic Quran without any crookedness, that they may guard (against evil).

The Holy Quran 41:3,
A Book of which the verses are made plain, an Arabic Quran for a people who know.

The Holy Quran 42:7,
And thus have We revealed to you an Arabic Quran, that you may warn the mother city and those around it, and that you may give warning of the day of gathering together wherein is no doubt; a party shall be in the garden and (another) party in the burning fire.

The Holy Quran 46:12,
And before it, the Book of Musa was a guide and a mercy: and this is a Book verifying (it) in the Arabic language that it may warn those who are unjust and as good news for the doers of good.

As we see from the ten verses above, Allah has a specific message that he wants to imprint on our minds and hearts by the adjectives which he brings with the word Arabic in the same verses.  However, let us not rely on our own assumptions or interpretations as I can already hear the arguments that may arise that, yes, it may be that it was revealed in Arabic because the people of the time were Arabs and how could they understand another language but today we come from many different nations and tongues.   So let us continue by looking at a clear hadith from Imam Jafar as-Sadiq (as). 

Imam Sadiq (as) said: 
"Learn Arabic, which is the word of Allah, and Allah has spoken to His servants in that language (the meaning of the Qur'an), and speak your jaws in Arabic and pronounce the end of the words clearly".  (Al-Khesal. Vol 2. P 258) 
In this above tradition, we see that the words of Imam As-Sadiq (as) are not advising or recommending us towards an action or a behavior, rather the words are decisive - a command.  What is our Imam telling? 

He says: "Learn Arabic", these are final and conclusive words from the sixth Imam (as).  He further tells us that Arabic is the word of Allah, he does not say the Quran is the word of  Allah but Arabic itself.  He tells us that Allah has spoken to His servants in Arabic "That language" and finally, he explains the physical aspect of the recitation - how we should recite in Arabic? "Speak your jaws in Arabic and pronounce  the end of the words clearly."

The above tradition coming from the Sixth Imam himself should also instill into our hearts that there is a science to the recitation of the  Arabic Quran and when something has a science, then there is a cause and an effect.  By mentioning the jaws,  we see that there is some physical benefit for our actual body that comes from reciting the Holy Qur'an in Arabic but what more does he tell us about this recitation?
The following tradition, answers this question.

Imam Jafar As-Sadiq (as) said "Try your best to read the Qur'an correctly in true Arabic pronunciation in the same way that Arabs read it." 
p 270 The life of Imam Al-Sadiq (as) Allama Baqir Sharif al Qarashi.

By the mentioned verses of the Holy Quran and the clear tradition (without even touching on the benefits of Arabic), there should be no doubt left about the actual command from our Imams and the guidance in the words of Allah himself that although we must understand the Holy Quran (reading in our native tongue), still there is nothing that can replace the function and role of the word of Allah in His own language.
 

The foundation of the holy religion of Islam is built upon the belief in monotheism, to the extent that without its acceptance, one cannot be called Muslim at all. This fundamental axiom is basically defined as the fact that God exists and that He is the only one; in other words, one must not only testify to the existence of a creator, a divine source, and a higher power, but also to His absolute uniqueness and singularity.

Is Human Able to Know His God?

We might wonder if we are able to understand or imagine God’s existence, the answer is yes but in quite a different way than other things. The concept of a divine source is philosophical and abstract; therefore we cannot feel or imagine it tangibly and vividly, however, our mind can understand such concepts by a kind of rational investigation and scrutiny in a general way.

How Can Human Beings Realize God’s Existence?

There are some specific ways to understand the existence of God based on Islamic doctrine, including “innate disposition”, “scientific or pseudo-philosophical reasoning” and “philosophical reasoning”.

Innate Ideas

Perhaps the easiest form of realizing God’s existence is with the use of “innate idea” which is present in every human being. According to Islamic teaching, all of us have some desires and characteristics with which we were born and that we unconsciously seek in our lives.

One of the most important inborn desires in human beings is the yearning for a God and creator; in other words, every person with his/her special creation and distinctive spiritual characteristics knows his/her God without needing any exterior knowledge. Many psychologists have claimed the existence of a hidden self, called the unconscious, which contains the innate and unknown desires of human beings; the desires that control their actions and influence their decisions. The force in the search of God, also, can be traced in this part of the human mind.

Pseudo-philosophical Reasoning

The reasons that are mentioned under this division include the “Teleological Argument”, “Causal Argument”, “Occurrence Argument” and “Guidance Argument”.

Teleological Argument

According to “Teleological Argument”, a comprehensive and efficient system is the one whose components are in balance and harmony and are ordered in a way to achieve a certain goal. If we consider the universe as an enormous system with complex functions and a web of relations, we could easily notice its sophisticated order and discipline.

Every element in this world is built with a kind of inner structure that enables it to do its job on a regular basis. For sure, this regularity has not happened accidentally. For this huge system to work properly,  a wise and powerful creator is required, one who is aware of every incident that takes place in the universe and has control over them.

Occurrence Argument

Based on this argument, this world and all other creatures had not existed before and came to be at a specific point in time. Consequently, since they have occurred and started to exist, they need a creator for their occurrence.

When we look around, we find ourselves surrounded by things whose existence is depended on something else, they go through changes – for better or worse-, and they are described concerning other things – i.e., their attributes are relative. We may first try to justify each incident by another one; however, ultimately we will realize that the summit of this chain must be a higher force who is unique and untainted by any flaw and inconsistency.

Furthermore, everything in this universe –including the universe itself- has initiated and will be terminated at a specific time; in other words, nothing in this world is infinite, and everything is born from its own kind – e.g., A human from a human, a horse from a horse, etc.

Thus the universe cannot be created spontaneously and out of itself or from a pile of dust, an animal or a tree, since the origin of every living creature is always another living creature. If we suppose that every kind of creature gains its existence from single or multiple origins, or consider the initial origin of them an ameba, then again we are faced with this question that how this ameba has been created. Here we arrive at this conclusion that there is a single, omnipotent, divine source who has caused the life on earth [i].

Guidance Argument

While “Teleological Argument” tries to prove Monotheism with regard to the complex inner structure of the creatures in the world that makes them capable of being in line with their role and objective in the universe, “Guidance argument” focuses on what these creatures actually do and how they do it.

Based on this argument, the creatures in this world, after being perfectly created, are guided by a mysterious insight and intelligent force through their course of actions. However, the path that they follow in their deeds is the result of an external cause, rather than their own built-in features. This sophisticated outer force is no one other than God, the one and only. 

Causal Argument

The “Causal Argument”, also known as the principle of causality, is one of the primary propositions known to people in their ordinary lives. This principle states that there is a cause for everything. In other words, every single thing that happens and every single effect, or existence, has a cause. But there must be a start to this series of events. It is believed that the beginning of this chain is a power, which is beyond all other powers and can cause everything to exist.

Philosophical Reasoning

This kind of reasoning, which is totally rational and philosophical, is based on the study of the existence and the existent. Briefly, philosophers claim that the existence of a “Necessary Being” [ii] is essential; meaning that if the “Necessary Being” did not exist, nothing would have started to exist and since there are things here, then a “Necessary Being” must certainly exist.

Why is God One and Unique?

First of all, as we said before, the creator of this world should be infinite and eternal. Accordingly, we cannot consider a like for an infinite being, since He is dominant over everything and no time or place is empty of Him. Furthermore, plurality necessitates a difference; that is two beings are separate if one has something that the other lacks, so they cannot be considered perfect.

Secondly, since God is an absolute and pure being, then we cannot find any incongruity in Him, and thus there is no need for another being to make amends for His inconsistencies.

Moreover, if there were two “Necessary Beings”, they must have had a gap or lapse among themselves. Consequently, the existence of a third being becomes crucial, and this process goes on endlessly.

Finally, the unity of the universe and its oneness and the fact that there exists no inconsistency and malfunction in the elements of this world, lead us to look for a single and unique being as its creator.

To conclude, monotheism (Tawhid) as the main entry to the religion of Islam which needs to be understood rationally and then fully accepted, rejects any dualistic, Trinitarian or polytheistic beliefs. This axiom is not only the cornerstone of the other Islamic axioms but also a necessity for practicing the practical principles of the religion. Even though individual investigation and understanding will bring faith in monotheism, this belief will not be complete without total acceptance of prophethood (Nubuwwah), and this takes us to the next axiom.

Notes:

[i]. Charles Darwin, the well-known English naturalist, and geologist, on this matter explicitly states that “life had been occurred through a divine breath.”

[ii]. There are two sorts of existent entities: those that exist but could have failed to exist, and those that could not have failed to exist. Entities of the first sort are contingent beings; entities of the second sort are necessary beings [1].

Reference:

1. God and Other Necessary Beings