Purify the intention is one of the cornerstones of acts of worship in this deen that Allah has sent to us. When you have a pure intention and when you really would like to do something for Allah and you want to please Him, you will make sure you’re conscious about everything else.
You purify your intention when it’s done solely for Allah to please Allah.
Then what happens? You begin to become conscious of the type of person you are.
A person who’s sincere would easily be able to work on their jealousy, their hatred, their ill feeling, the qualities of the heart that are negative.
Islam is all about being sincere. Sincere to Who: Be sincere with intension to Allah by worshiping Him alone