Although the whole Book of Holy Quran is a complete guide for its readers, but it contains certain small Chapters which weigh more in their implication from the longer ones. Surah Fatiha is the opening of Furqan e Hameed and is a highly significant supplication for attaining the righteous path of Islamic conviction. Surah yousaf is about the story of prophet Yousef life. Similarly, there are four small sections at the end of this Sacred Scripture which are generally known as “Four Qul”.

These 4 Surahs of Quran are Al-Kafirun (109), Al-Ikhlas (112), Al-Falaq (113) and An-Nas (114). They are usually called the shielding Chapters in the entire Quran Pak. First two defend one from committing Shirk (Considering someone else equal to Allah), while the following ones defend against many evils of this world.
It means that these four Chapters are great means of attaining shield from all kinds of evils present in this world.
In short, four Quls are very heavy in the magnitude of their benefits that they generate for the believers.