A similar (favour have ye already received) in that We have sent among you an Messenger of your own, rehearsing to you Our Signs, and sanctifying you, and instructing you in Scripture and Wisdom, and in new knowledge.
Truly he succeeds that purifies it
But those will prosper who purify themselve
O Lord, give me my soul and purifies its aim if it is their best
The above mentioned verses of the Holy Quran and the Hadith of our beloved Prophet (Peace be upon him) all talk about 'Tazkiya'. The term 'Tazkiya' literally means to purify both the external (apparent) and internal (hidden) impurities. As far as external impurities go, the average Muslim is well acquainted with them. The internal impurities are many, some of them being disbelief in Allah, the ascribing of partners to Him, reliance on beings other than Him, Arrogance, Envy, Malice, Materialism etc.
With regard to these internal impurities one must always bear in mind two essential things. Firstly that Allah Ta'ala has always made two ways available to man by which he is able to attain purification; the first being the Holy Books and the second the Prophets sent down to teach these Books. Just as He did not consider that the Books without the Prophets would suffice, He likewise did not consider the sending of the Prophets without the books to be sufficient, thus both were sent simultaneously. This custom of Allah Ta'ala and the testimony of the Quran which resulted in the simultaneous running of both these paths for the well-being and welfare of mankind, flung open the doors to a Higher Knowledge and taught us that man's rearing and upbringing can only be properly and successfully achieved if both things go hand in hand. For a book cannot be a teacher by itself nor can a man be a guide without a book. Perfection is achieved when a guiding human hand combines with Heaven-sent guidance, for after all man is man's best mentor and guide.
For this very reason, just like the spread of Islam started with both a Prophet and a Holy Book, future generations likewise benefited from the Shariat combined with a chain of pious men.
O ye who believe! Fear Allah and be with those who are true (in word and deed).