When you go to bed at night and you are feeling peaceful in your thoughts, it normally would carry over into a more peaceful sleep. When you go to bed at night and you are all worried and agitated, it is going to be hard to fall asleep. To a certain extent the moment of death, your last thought - according to Buddhism - will put forward what is going to happen in the next moment, which is your next birth. So if you are peaceful, loving and kind in the moment of death, that will give you a favorable rebirth. If you are angry, full of fear whatever at the moment of death, then that puts the anger and fear into your next rebirth. According to your Kamma, your good Kamma and your bad Kamma, if you can die with peaceful thoughts, then that pushes your good Kamma to fruit first. If you die with angry thoughts, that pushes your bad Kamma to fruit first. So this is how important it is at the moment of death- your last thought.
This is another reason why we train with wise reflections, train your thoughts, train your thoughts, train your thoughts... If you only do concentration work in which we block out thoughts, concentration on candles, a flame, a mantra or anything else, the breath as well, if you only block out thoughts, then you haven't trained yourself to bring anything up at the moment of death. So this is important, to train your mind in wise thoughts.
The monks and nuns in Thailand, in fact in all Buddhist countries, they train in the chanting. This is really the same work that we are encouraging you to do with the wise reflections. The monks and nuns when they are chanting, they are reciting the teachings. Exactly the same, every day, every day, every day...They may recite the qualities of the Buddha, the Dhamma and the Sangha, they are going to recite that death is coming, they are going to do some Compassion/Lovingkindness reflection, they are going to reflect on Kamma, they are going to do very similar things to what you are doing, it is Pali words from the scriptures.
So by training the mind over and over and over to think good wise thoughts, then those thoughts can come up more quickly at any time during the day. It is amazing how often I am talking with a Thai and all of a sudden they just say something exactly from a chant. It is so ingrained in them that they bring up the exact same words and they really firmly believe it because they have chanted it over and over. This is another reason why we encourage you to do reflection in a brief form at the beginning of every period so it sinks in deeper and deeper and deeper, and it might come up at the moment of death.