There are many Muslims who believe in and apply the Qur'aan, however, they do not regularly sit and read it. They may have enough of it memorised to perform their prayers, but beyond that they do not have much knowledge of the Qur'aan. This lackadaisical approach to reading the Qur'aan is, sadly, not that uncommon. The Standing Committee of Scholarly Research and Religious Rulings in Saudi Arabia received the following question and others similar to it:
"What is the ruling concerning reading the Qur'aan, is it obligatory or recommended, as we have asked about its ruling and some have said that it is not obligatory. [In other words] if a person reads it, there is no harm and if he does not read it, there is no [sin] upon him. If that were the case, then many would leave it. So what is the ruling concerning avoiding it and what is the ruling concerning reading it?"
The response of the committee made of Shaykh 'Abdul 'Azeez Ibn Baaz رحمه الله, Shaykh 'Abdur Razzaaq al-'Afeefi رحمه الله, Shaykh 'Abdullaah Ibn Ghudayaan رحمه الله and Shaykh 'Abdullaah Ibn Qa'ood رحمه الله was,
"What is legislated with respect to a Muslim is for him to keep up in reciting the Qur'aan and to recite it often according to his ability, in compliance with the generalness of the command in Allaah's سبحانه و تعالى words,
'Recite, [O Muhammad صلى الله عليه وسلم], what has been revealed to you of the Book [the Qur'aan] and establish prayer.' [Sooratul-'Ankaboot, 29:45],
'And recite, [O Muhammad صلى الله عليه وسلم], what has been revealed to you of the Book [the Qur'aan] of your Lord (i.e. recite it, understand and follow its teachings and act on its orders and preach it to men).' [Sooratul-Kahf, 18:27],
and His statement about His Prophet صلى الله عليه وسلم,
'[Say, O Muhammad], "I have only been commanded to worship the Lord of this city [Makkah], Who made it sacred and to Whom [belongs] all things. And I am commanded to be of the Muslims [those who submit to Allaah]. And to recite the Quran." So whosoever receives guidance, receives it for the good of his ownself, and whosoever goes astray, say (to him): "I am only one of the warners."' [Sooratun-Naml, 27:91-92].
The Messenger of Allaah (may Allaah exalt his mention and grant him peace) also said, 'Recite the Qur'aan, for it will come as one who intercedes for its companion on the Day of Resurrection.' Recorded by Imaam Muslim رحمه الله in his Saheeh. [The Muslim must also] avoid any form of avoiding and cutting off from it in any way as mentioned by the scholars. [Then the reply quotes Imaam Ibn Katheer's رحمه الله commentary to Sooratul-Furqaan and the meaning of mahjoor similar to the discussion given above]." 
It may be the case that some sincere Muslims find it difficult to read the Qur'aan. Shaykh Saalih al-Fawzaan حفظه الله was asked the following question: "I try to read the Noble Qur'aan and I very much love the Book of Allaah سبحانه و تعالى but I find it very difficult for me. I am not able to complete the recitation. What is the solution?" Shaykh al-Fawzaan حفظه الله replied that first the person must seek refuge in Allaah سبحانه و تعالى from the accursed Shaytaan, as Allaah سبحانه و تعالى has mentioned in Sooratun-Nahl, 16:98-100. That is the most important first step. Secondly, the person should not simply read the Qur'aan but he should study it and ponder over its meaning. This will increase his fear of Allaah and his desire to read more of the Qur'aan. The reader's concern should not be to finish a certain portion of the Qur'aan or a certain soorah but it should be to read, understand and ponder over the meanings of the verses. 
There is no question that the one who believes in the Qur'aan and applies it whenever he is told of what it contains is in a better position that one who reads the Qur'aan and does not apply it. Indeed, he is even in a better position that the one who memorises the Qur'aan yet does not apply it. However, he may be missing the great effects that the Qur'aan could have on his faith and his life. By constantly reading the Qur'an, even the same soorahs over and over again, one may be enlightened and get some insight that he would have missed otherwise. Hence, those who believe in the Qur'aan and apply it yet do not take the time to read it are perhaps preventing themselves from getting even greater benefit from the Qur'aan. Such people should turn to the Qur'aan and read it and allow it to have its full effect upon them and try to gain as much guidance from it as they can.
Furthermore, when one does not read the Qur'aan on a regular basis, it becomes easy for him to forget some of the teachings of the Qur'aan or he may remember those that he applies on a regular basis but he may forget those that he needs for specific occasions. In fact, the Messenger of Allaah صلى الله عليه وسلم said, "Attend to this Qur'aan [and keep refreshing your knowledge of it], for by the One in Whose hand is the soul of Muhammad, it is more liable to escape [from one's mind] than a camel that is tied down." 
Based on this hadeeth, Shaykh Saalih al-Fawzaan حفظه الله concludes that a Muslim should recite the entire Qur'aan, at the minimum, at least once a month. 
Allaah knows best. 
 Ahmad Ibn 'Abdur Razzaaq ad-Darweesh, ed., Fataawaa al-Lajnah ad-Daa'imah lil-Buhooth al-'Ilmiyyah wal-Iftaa' (Riyadh: Maktabah al-Ma'arif, 1412 A.H.), vol. 4, pp. 66-67.
 Shaykh Saalih al-Fawzaan حفظه الله: Muhaadhiraat fil-'Aqeedah wad-Da'wah (Riyadh: Daar al-Aasimah, 1415 A.H.), vol. 2, p. 306.
 Recorded by Imaam Muslim رحمه الله.
 Shaykh Saalih al-Fawzaan حفظه الله: Muhaadhiraat fil-'Aqeedah wad-Da'wah (Riyadh: Daar al-Aasimah, 1415 A.H.), vol. 2, p. 296.
 How to Approach and Understand the Qur'aan, pp. 56-59.