The 3rd verse of this Surah is believed to be the last verse revealed to the Prophet, where Allah (SWT) says “Today I have perfected your religion for you, completed my favor upon you, and approved Al-Islam as a way of life for you.” 

This Surah was revealed in Madinah soon after the Treaty of Hudaibiyah either towards the end of the 6th year of Hijrah or at the beginning of the 7th year of Hijrah.  It was revealed at the time when the last effort of the Quraish to suppress Islam was defeated in the Battle of the Ditch.  Now Islam was not just merely a creed which ruled over the hearts and minds of people, but it was now a state which was regulating the lives of people.  This Surah provided the guidelines to the believers so their social behavior, conversation, dress, way of life, and culture could take a definite shape of its own.
 
There are six main points discussed in this Surah:

• All obligations whether they are divine or human should be fulfilled. When we have a pledge or promise or sign a treaty we must abide by it. Also Allah gave some rules for life to keep us clean and sober.  Cleanliness of the body, living with justice, being upright and moral, avoiding sin, corruption and superstition, and doing the deeds of piety and righteousness are important rules and principles and must be observed.  Now that the Muslims had become a ruling body, there was a danger that power might corrupt them.  So Allah warned them over and over to guard against the wrong behavior that mislead the Jews & Christians before them.
• Message to the People of the Book, i.e. Christians and Jews, to recognize the truth.  Allah's punishment comes on those who reject Allah's rules and knowingly violate them.
• The story of the two children of Adam is told.  This story has many lessons. Sometime even your brothers become envious of you and they harm you.  Just and righteous people sometimes suffer at the hands of their own family members, but God's judgment also comes. The righteous under no situation give up right attitude and behavior.
• Muslims must deal with justice with all people.  Justice should be impartial, even to their enemies they must be just.  However, relations among Muslims themselves should be deeper.  There should not be only justice but also love, brotherhood & sisterhood, care and concern for each other.
• Enjoy the good things that Allah has given, but guard against excesses.  Do not indulge in swearing, gambling, intoxicants, superstitions, violation of the sanctities of the Sanctuary of Allah (the Ka'bah).
• Jesus -peace be upon him- was a great prophet of Allah. He performed many miracles, but his teachings were not followed and they were corrupted after his departure from this earth.