"Blessed are the pure in heart, for they shall see God." -Matthew 5:8
Jesus said the pure in heart will see God.
The heart of man is naturally unclean not pure. We can't even make it clean on our own doing. It can only happen through the blood of Jesus Christ.
"Create in me a clean heart, O God; and renew a right spirit within me." -Psalm 51:10
A person with a pure heart isn't a perfect person who does no wrong. Rather, it is a person who wants to serve God and please Him in all that they do. They may stumble, but they are striving to live a holy life. A pure heart comes down to the matter of your intentions.