Māra is the deity ruling over the highest heaven in the sensuous sphere (kāmāvacara). This is the heaven of the paranimmitavasavatti-devas, "deities wielding power over the creations of others." Māra followed the Buddha, looking for a weakness in him, for six years before his Enlightenment and one year after it. He also tried to persuade the Buddha not to teach others the method of putting an end to suffering. He reappeared again before the Buddha's Parinibbāna and urged him on, not wanting him to continue teaching the way out from suffering.
Māra is seen as the Tempter who encourages beings to believe that the satisfaction of sensual desires is the highest form of existence ("eat, drink and be merry"). There are many people who agree wholeheartedly with this and they live their lives accordingly.
The Buddha, on the other hand, says, "eat, drink and be merry" is all very well, but "tomorrow we die". That is, in order to enjoy the pleasures of the senses, we have to have senses. In order to get senses we have to be born. When we are born, we don't only enjoy sense pleasures, we also get sickness, old age and death. The only way to avoid the suffering which is experienced between birth and death is not to be born again.
If we take the view that death is the end of it all, then we could say, " Since we only live once, we might as well make the most of it and satisfy the pleasures of our senses as much as we can while we still have them."
If "we only live once", this is not unreasonable. But the Buddha says that we don't only live once but many times. Every death is followed by a new birth until we put an end to the desire for birth. And each new birth depends on how we have behaved in our previous birth i.e. our karma. We can go up or down. We can even be reborn as animals.
The word "Māra" has as its root an Indo-European syllable that means "Death". The significance of this is that if we go along with Māra's "eat, drink and be merry" and get ourselves senses by being born, we are trapped under Māra's Net and "we die". Over and over again.
We are, of course, free to choose between Māra's view and the Buddha's. Those who enjoy a life of sensual pleasure, find Māra's view very tempting. Those aware of a larger picture see the suffering inherent in birth, sickness, old age and death. To these, the Buddha's view offers a lasting prospect of happiness and peace.
There is the Great Māra.
There are māras (you meet them everyday).
There are the māras in the mind; these appear as thoughts and mental images.
And sometimes as voices.
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