No kind action ever stops with itself. One kind action leads to another. Good example is followed. A single act of kindness throws out roots in all directions, and the roots spring up and make new trees. The greatest work that kindness does to others is that it makes them kind themselves.
The quote presents kindness as something that extends beyond a single interaction. A helpful act may influence the person who receives it, who may then behave similarly towards others. The image of roots spreading and producing new trees suggests that the consequences of one action can develop in directions that are difficult to predict or measure.
The central idea is that example can shape behaviour. Kindness is valuable not only because it benefits its immediate recipient, but because it may encourage further kindness and gradually affect a wider community. The passage therefore treats moral conduct as socially contagious: people learn partly from what they observe and experience. Its broader ethical point is that individual actions can contribute to shared norms, making generosity, consideration and cooperation more likely to be repeated by others.