One of the beatitudes says, "Blessed are the pure in heart, for they shall see God." Purity of heart is an interesting thing. Back in ancient times, "heart" meant more than just emotions. It meant the core or essential part of a human, which included thinking, feeling and willing. If we follow through with the metaphor that hearts can be pure or impure, how are we to understand that?
Perhaps the easiest way is to think of a glass of dirty water. If we take a glass of pure water and stir in some dirt, we now have a glass of dirty water. In a certain sense, the water is inherently pure--the dirt is incidental and has never been a part of the essential nature of water. They are just mixed together. Hearts are similar. If it wasn't so, then our hearts could never be purified. In my opinion, the whole notion that people are inherently evil/flawed, is fundamentally problematic. If our hearts were inherently evil, they could never be purified. Our imperfections are part of our makeup, but not inherent to our essentially pure nature.
In the process of purification, we may need aid. I think of Jesus, Buddha, Krishna, and other great saints and sages as divine friends who remind us of our natural purity, and then help us along the way of purifying the heart. It is interesting that a famous quote of the Buddha is, "To avoid all evil, to cultivate good, and to purify one's mind—this is the teaching of the Buddhas." In the ancient Pali language, the word translated as "mind" is c(h)itta, which actually has a more general meaning of heart-mind. So, it could just as easily be translated as "purify one's heart", if this more general meaning of heart is used. I've always found that interesting.
Of course I totally ignored the whole "for they shall see God" part. Interestingly, just this evening I was reading Tulku Urgyen Rinpoche's As It Is, Vol 1, and came across this quote: "Phenomena manifest in both pure and impure forms. Impure phenomena is what is experienced in this world. Pure phenomena is when there is no dualistic grasping." So, from a Buddhist perspective, one could say, "Blessed are the pure in heart, for they shall see pure phenomena."