It seems that gratitude starts with morality and progresses to blissful gratitude.
Initially, one is simply taught how to express gratitude, and eventually, one comes to understand the meaning of gratitude itself.

The line between the common sense understanding of gratitude taught in general education, ethics, or the Hinayana Buddhist teachings, and true gratitude, becomes blurred. This is like the missing link in the evolutionary path from apes to humans, where the path between moral gratitude and true gratitude becomes unclear and acts as a missing link.

On the other hand, from the perspective of esoteric Buddhism and spirituality, it seems possible to explain the connection between these. The beginning and the end are both gratitude, but the space in between can be bridged by spiritual explanations.

First: (Moral) Gratitude
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Missing Link
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Last: (Spontaneous) (Blissful) Gratitude

The spiritual stages are as follows:
- (Moral) Gratitude → In terms of Yoga, it corresponds to the Yamas and Niyamas of the Yoga Sutras, or a part of the Hinayana Buddhist teachings. Understanding and practicing what should be done and what should not be done.
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- Healthy lifestyle. This is the stage of increasing "prana" (energy) and becoming revitalized by reviewing diet, habits, and living environment (as described in Yoga).
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- Meditation in spiritual unity. The so-called "zone." A state of bliss. Purification of thoughts, reduction of distractions.
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- Awakening of Kundalini, activation of chakras (from the bottom up).
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- Kundalini fills the Sahasrara (crown chakra) and reaches a state of stillness.
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- Connecting with the Higher Self from behind the Anahata (heart chakra).
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- Kundalini becomes easier to reach the Sahasrara.
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- The Higher Self and Kundalini become one, including the Ajna (third eye chakra), Sahasrara, and Anahata, leading to bliss. It feels like being enveloped in light.
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- A spontaneous feeling of gratitude arises from the heart, simply saying "thank you."

Depending on the state of the day, one may proceed through the stages from a little earlier, but sometimes, one can spontaneously feel gratitude and say "thank you" simply by sitting down. At other times, one may need to first resolve energy blockages in a certain energy channel (nadi in Yoga), which can manifest as muscle pain or stiff shoulders.

Even when proceeding through the stages, it can be done in a much shorter time than before. Previously, one would only reach the previous stage, but recently, one has been able to progress to the stage of gratitude. One didn't even know that such a stage existed until one reached it, and one only recognized the existence of this stage of gratitude upon reaching it. However, it is not yet clear whether this is the final destination or if there are further steps. Nevertheless, it is unlikely that this is the final destination, and based on memories of past lives, it seems like there might be other subtle things. Therefore, I would like to further explore this meditation.

When written down, it seems quite simple, but there were many things happening at each stage.