The Importance of Giving
"If beings knew, as I know, the results of giving and sharing, they would not eat without having given, nor would the stain of miserliness overcome their minds. Even if it were their last bite, their last mouthful, they would not eat without having shared, if there were someone to receive their gift. But because beings do not know, as I know, the results of giving and sharing, they eat without having given. The stain of miserliness overcomes their minds."
— Iti 26 (Quote from the Buddha from the Pali Cannon)
Because the Buddha was able to see his own and other people's Karmic stream, he was able to understand just how important and impactful each moment of one’s life was. He could see how one word or action would set off a chain of events that greatly influenced how a person’s future would unfold.
In addition to this, he knew the strength of habit that both generosity and stinginess (basically fear) can have in the hearts and minds of human beings. Generosity begets generosity and stinginess begets stinginess. He knew the importance of feeding wholesome habits and not feeding unwholesome habits.
So when you are faced with a decision to give or not give, don’t just look at the decision from this moment's perspective, but consider what you will be setting in motion, and what impact that will have on your future. Both in this life and subsequent ones.