What does it mean by having a kind heart, say kind words and do kind deeds?

Our every thought needs to be of benefiting all sentient-beings. Not only in our behavior should we never hurt any beings, but also we should never give rise to a single hostile thought or say anything that can cause distress to others. If we can truly follow this teaching, then in our daily lives no matter what we do, there will be great goodness, great gentleness. This is the way to truly influence people, with loving-kindness and compassion.

Using physical force to try to solve problems will not only create enemies but will also generate the cause to be born into the hell realms. By practicing in accordance with the teachings, we will achieve results for this way we will transform our minds. Since everything is a reflection of our minds, everything can be transformed by our minds. When we accord with the teachings, our thoughts will change for we will have let go of selfishness and our actions will be proper as we only have thoughts that benefit others.

(Adapted from http://www.amtbweb.org/tchet505.htm)