Blessed are the Pure in Heart
Eating organic food is a big health craze right now. No one wants to eat the stuff that's been sprayed with pesticides or pumped full of steroids and preservatives. Why? Because it's a proven fact that the extra stuff will contaminate our bodies and make us sick. When we eat food that man has messed with, we keep our bodies from functioning as God intended.
The same principle applies to our hearts. When we feed our hearts what the world dishes out, we keep them from doing what they were meant to do.
But when we focus our hearts on God's Word and worship God with our thoughts and actions, He will keep our hearts pure. Only then will our hearts be capable of doing what they were meant to do - help us see God.