One of the foremost duties of Rasulullah صلى الله عليه وسلم was the purification of heart,as mentioned in Surah Al Jumu'ah:

"He it is who sent among the unlettered ones a messenger(Muhammad صلى الله عليه وسلم  ) from among themselves, reciting to them his verses,purifying them(from the filth of disbelief and polytheism ) ,and teaching them the book(this Quran, it's laws and Jurisprudence ) and al-hikmah.(the Sunnah) And verily, they had been before in manifest error."
[Surah al-Jumu'ah 62:2]

Just witness the miracle of transformation after entering into the fold of islam (The name of religion of Muslims -Literally means 'Submission'):Although it was not possible for each and every new Muslim to know all the laws and tenets of Islam the moment he or she declared his / her allegiance to the Messenger of Allah Ta'ala صلي الله عليه وسلم ,there was total submission to the laws of Islam.

If we were to study their live ,we will find that in their acceptance of Islam,  there was immediate fulfilment of almost all the Ahkaam  (laws) of Shariah( code of Islamic law);which is very unique.

If a person has to accept islam today , at our hands, it would take us time teaching him even the basic laws and practices of Islam. This remarkable capacity and aptitude found in the Sahabah was due to the blessed Suhbah  (Companionship) of Rasulullah صلى الله عليه وسلم.