[ Picture of a river taken in Northern Area of Pakistan. To me it depicted purity, hence the inclusion.]
As Muslims not only physical cleanliness is required but cleanliness in all forms is to be attained. And that is your purity. Your soul, intentions and thoughts should be pure.
It's a saying of Holy Prophet (S.A.W) that, "Cleanliness is half the faith." Imagine the significance when it has been termed half of your faith! It's crucial that the thoughts and intentions we house in our cranium are pure as it is a well know saying that, thoughts become words. Words become actions. Actions turn into habit. Habits showcase character. And the character becomes your destiny.
Importance of cleanliness and purity can also be assessed through the fact that before observing prayer ablution is to be done. The soul's purity is in remembrance of Allah. And the mind's purity is in asking Guidance from Allah over and over again. Sometimes we get so caught up in the issues of this world and in praying for worldly things that we forget the most important prayer. That is the prayer to be on the right path, the enlightened path!
Purity can be achieved from meditation aswell and if we try over and over again to condition our brain into thinking pure thoughts.