satipatthana

Protection
If the nothing and obderving mind remains face-to-face with the object of observation for a significant period of time, the yogi can discover a grate purity of mind due to the absence of kilesas(mental defilements). This purity is the result of the second manifestation of sati-guardianship or protection from attack by the kilesas(arakkha paccupatthana).With sati present,mental defilements have no chance to enter the stream of consciousness.
Sati is likened to a doorkeeper because it guards the six sensedoors.A doorkeeper does not admit bad and destructive people;he admits only good and useful people.Sati does not admit unwholesomeness(akusala);it admits only wholesomeness (Kusala).By not accepting akusala,the mind is protected.
The proximate causes of mindfulness
The proximate causes for the arising of sati are:strong perception (thirasanna padatthana); and the four foundations of mindfulness(kayadisatipatthana padatthana).