The meaning of this sentence is that people's behaviors and thoughts will have positive or negative effects on themselves and others. If our hearts are full of positive emotions such as kindness, compassion, tolerance and gratitude, it will prompt us to do good deeds and do things beneficial to society, so as to get more positive feedback and returns.
In Buddhism, "goodness" refers to the mentality with positive qualities such as sadness, joy, humiliation and wish, while "blessing" represents all kinds of positive causal feedback, such as happiness, health, success, wisdom, merit and so on. Therefore, as long as you keep a kind heart and make positive behaviors, you can attract more blessings and good luck, and let yourself and others get more happiness and achievements.