Reflecting on impermanence and death in itself is not really a big deal, but thinking about it because of what follows after the death is important. If there is negative karma, then there are the lower realms of unimaginable sufferings, and this is something that can be stopped immediately.
We cannot be liberated from samsara within this hour, today, this week or even this year, but we can purify negative karma now, this hour today, and therefore stop being reborn in the lower realms if we die now, this hour, today. This is possible.
By remembering impermanence and death, karma and the lower realms of suffering, the mind is persuaded to use the solution of Dharma practice. Immediately the mind prepares for death. Immediately it purifies the heavy negative karmas that cause one to remain in the lower realms, where there are unimaginable sufferings and no possibility to practice Dharma.
Whenever there are problems in our lives it is always good to remember the lower realms of suffering. We can't stand the problems we have now, but the lower realms of suffering are a zillion, zillion, zillion times greater, like the sky. If we put together all the energy of fire, no matter how hot, it is cool compared to one tiny fire spark of hell. All the energy of this human world's fire put together is cool compared to one tiny fire spark of the hell realm. Like this, it's always good to make a comparison.
Beings possessing a human body who haven't met Dharma, no matter how much wealth they have, no matter how may friends they have, no matter how much they appear to be enjoying their lives, in reality are only living with hallucination; they are living with wrong concepts, so many piles of wrong concepts. They are not aware of what is happening to them, they are not aware of their own life. They are not aware of the powers of their hallucination, the piles of wrong concepts that compel them to create the causess of samsara and the causes of the lower realms. They don't have the opportunity to plant the seed to be free from samsara, to cut the root of samsaric ignorance, because there is no understanding of emptiness, no opportunity to meditate on emptiness.
If a person has a good heart, a sincere mind, and gives some help to others without expecting any results, then maybe they create some pure Dharma—but that's very rare; otherwise not. Usually people live the life only with a worldly mind, particularly attachment, clinging to this life. They use the whole human life, the precious human body and all their education just to create additional causes to go to the lower realms.
This is what is happening in every day life. For the entire life people act like a moth attracted to the flame, completely hallucinated, completely deceived, not knowing the flame will burn, that it is completely other than what it appears. Even though they get burned, while they still have the power to fly they will continue to go towards the flame.
It is exactly the same with a fish and a baited hook. The fish does not know that there is a hook that cheats, leading to death and unbelievable suffering. Having no idea of the danger, it is constantly being drawn with strong desire toward the hook baited with a piece of meat. The result that the fish experiences is completely other than what it expected. Once caught, there is no way to get away alive.
Following the dissatisfied mind, desire, the worldly mind, brings exactly the same result. Once sunk in the quagmire of the activities of this life, it is difficult to escape the hundreds of different problems, emotional pains of the mind and of the body that come from this one root, the dissatisfied mind, desire, attachment, clinging to this life. All we are doing is making samsara longer by creating karma; we are making a donation, a contribution to samsaric suffering, making it longer and longer. And then, of course, there are the sufferings of the lower realms, which are difficult to get out of.
It's the same with the way in which an elephant can be caught. A female elephant is used as a lure, the male elephant becomes crazy with desire and as a result, becomes trapped inside a cage. What was expected in the beginning was happiness, but what was received in the end was something else, something completely frightening.
All these examples show us the way in which samsara and the samsaric perfections cheat us, that they are not to be trusted. Therefore always remembering impermanence and death becomes so essential. Reflecting on impermanence and death makes life highly meaningful, and so quickly and so powerfully destroys the delusions and seed imprint. It is very easy to meditate on and one can cease the delusions. It leads one to begin to practice Dharma, and to continue and complete the practice.