There are people in our life who have changed us. Changed us in ways that we couldn't imagine what our life would be like had we not been touched by their grace. We would be entirely different people.
They are people whose words have impacted our mind, whose presence has opened us up and whose kindness has permeated our heart. They could be people we have known for many years, or even those who we knew for a brief moment in space and time. Those people are our greatest teachers. They've changed us, stuck with us even when they are no longer around. They have given us a gift that is timeless and inexhaustible.
We can never repay our teacher's kindness. It is not possible because they have created a world that we could have never imagined even for ourselves. Their gift to us has created something that didn't exist before and the only way that we can begin to repay their kindness is to share it. Increase it and spread it throughout the ten directions.
You can never be sure when a gift will create a new world, so give generously and dedicate all of your actions to the benefit of beings.