*Surah Introduction
The Surah answers some questions that the Mushrikin of Makkah posed to the Prophet (saw). The answers came in a very clear way and also challenged them to accept the message of Islam. In this Surah we have the stories of: the People of the Cave, the man who had two gardens and was very proud of himself, Prophet Moses with a special teacher, Dhul-Qarnain a pious ruler. These stories are told to emphasize the value of faith, knowledge and patience and the relativity of time.
Sections:
The upright message of the Qur'an.
The Companions of the Cave.
The proof of resurrection.
Always remember Allah. Every thing depends on Allah’s will.
The parable of an ungrateful person and a grateful person.
Wealth and children are only a passing show.
Satan and his progeny they are the open enemies of human beings.
Allah's mercy is available all the time.
Prophet Moses' search for a teacher.
The pious ruler Dhul Qarnain. Gog and Magog
The real losers and winners.
The Surah is named after the Cave which the Youth retreated to for protection, as mentioned in Ayat , "And when you have withdrawn from them and that which they worship other than Allah, retreat to the Cave.... " [18:16]
There are 110 Ayat in this Surah.

*Central Theme
Theme 1: Protection from Fitnah [trials and tribulations]
Fitnah in religion: In the story of the youth and their tyrant King (18:9)
Fitnah in wealth: In the story of the one with two gardens (18:44)
Fitnah in knowledge: In the story of Musa and Khidr (18:82)
Fitnah in governance: In the story of Dhul-Qarnayn (18:83)

*Connection between the beginning and the ending of the Surah
* The begining and end of the Surah mention the Revelation and Words of Allah. Towards the end of the Surah, Allah says, "Say, "If the sea were ink for [writing] the words of my Lord, the sea would be exhausted before the words of my Lord were exhausted, even if We brought the like of it as a supplement." [18:109] and in the begining of the Surah, Allah says, "[All] praise is [due] to Allah, who has sent down upon His Servant the Book and has not made therein any deviance..." [18:1]
* In the begining and the end of the Surah there is glad tidings for the righteous Believer - "... give good tidings to the believers who do righteous deeds that they will have a good reward." [18:2] and in the end of the Surah, "Indeed, those who have believed and done righteous deeds - they will have the Gardens of Paradise as a lodging," [18:107]
* Similarly, there is a warning to the disbelievers in the begining and the end of the Surah. "[He has made it] straight, to warn of severe punishment from Him..."[18:2] and in the end, "And We will present Hell that Day to the Disbelievers, on display,Those whose eyes had been within a cover [removed] from My remembrance, and they were not able to hear.Then do those who disbelieve think that they can take My servants instead of Me as allies? Indeed, We have prepared Hell for the disbelievers as a lodging." [18:100-102]