What does it mean to be pure in heart? Purity suggests cleanliness; something that has not been even slightly dirty.
The problem is we were born with a sinful heart, so how can it be made pure? The only way to clean a sinful heart is by confessing our sins to Jesus and asking for forgiveness. His sacrifice paid the price for our sins, and he will wash our hearts clean.
We have to keep our hearts focused on God.
"Becoming a Better You" 