"My strength is as the strength of ten because my heart is pure."
Alfred, Lord Tennyson
Having a pure heart would be something we'd all want. Having a heart free of worries, guilt, and resentment is something we truly long. Because when you're full of hatred and dismay, you feel weak and hopeless. You can't do things properly. One projects what they're feeling inside. Thus, feeling weak and hopeless, you'll may someone feel just the same.
In other words, feeling full joy and hope, the people revolving around you will feel the same.