In whatever Teachings and discipline The Noble Eight Fold Path is not found, no Ascetic is found of the first, the second, the third or the fourth grade. But such Ascetics can be found of the first, second, third, and fourth grade in a Teachings and discipline where The Noble Eight Fold Path is found.

Now, Subhadda, in these Teachings and discipline The Noble Eight Fold Path is found, and in it are to be found Ascetics of the first, second, third, and fourth grade. These other schools are lacking of [true] Ascetics, but if in this one the Monks were to live the life to perfection, the world would not lack for Arahants.

(Reference: DN 16)

In this Teaching from Gotama Buddha, he shares the importance of The Eight Fold Path.

He explains that if a training discipline does not include The Eight Fold Path there will be no one who has attained the first, second, third, or fourth Stage of Enlightenment associating this to “the first, the second, the third or the fourth grade” much like a traditional school of education would have grades for Students to progress through.

The Path to Enlightenment and The Buddha’s Community of Practitioners is much like a “school” of Students learning, reflecting, and practicing Teachings to progress through Stages of Enlightenment much like one might progress through a traditional school system to higher levels of knowledge and education.

Gotama Buddha explains that if a training discipline does include The Eight Fold Path and the Practitioner lives life to the ideal perfection of The Eight Fold Path, there will be no lack of Practitioners who would attain Enlightenment referred to as an Arahant. An Arahant is an Enlightened being.

In the first, second, and third Stages of Enlightenment, the mind is not yet Enlightened. It is not until the mind eliminates all of The Ten Fetters that one is considered an Arahant and, thus, the mind is Enlightened. An Enlightened mind will no longer experience any discontent feelings. In the first, second, and third Stages of Enlightenment, discontentedness has been significantly decreased, but not fully eliminated.

A Practitioner progressing to the fourth Stage of Enlightenment as an Arahant will no longer experience any discontent feelings. The mind will reside peaceful, calm, serene, and content with joy - permanently.