This teaching is from the section The Planes of Realization of the book “In the Buddha’s Words” by Bhikkhu Bodhi.

As long as sun and moon do not arise in the world, there is complete darkness. Similarly, as long as the Buddha has not arisen in the world, there is complete darkness, dense darkness.

As long as, bhikkhus, the moon and sun do not arise in the world, there is no great light, no great radiance. Then, there is complete darkness, blinding darkness. Neither are night and day discerned, nor months and fortnights, nor seasons and years.

But when, bhikkhus, the moon and sun arise in the world, there is great light, great radiance. Then, there is neither complete darkness nor blinding darkness. Then, night and day are discerned, months and fortnights are discerned, and seasons and years are discerned.

Similarly, bhikkhus, as long as the Tathāgata, the Arahant, the Perfectly Enlightened One, does not arise in the world, there is no great light, no great radiance. Then, there is complete darkness, blinding darkness. There is neither the declaration, nor the teaching, nor the describing, nor the putting forward, nor the revealing, nor the analysis, nor the exposition of the four noble truths.

But when, bhikkhus, the Tathāgata, the Arahant, the Perfectly Enlightened One, arises in the world, there is great light, great radiance. Then, there is neither complete darkness nor blinding darkness. Then, there is the declaration, the teaching, the describing, the putting forward, the revealing, the analysis, and the exposition of the four noble truths. Which four? The noble truth of suffering, the noble truth of the cause of suffering, the noble truth of the ending of suffering, and the noble truth of the path leading to the ending of suffering.

Therefore, bhikkhus, effort should be made to understand: ‘This is suffering’; effort should be made to understand: ‘This is the cause of suffering’; effort should be made to understand: ‘This is the ending of suffering’; effort should be made to understand: ‘This is the path leading to the ending of suffering.’

The four noble truths is the teaching that the Buddha shared the most during his 45-years of teaching career. Here, he is sharing the importance of understanding the four noble truths, reflecting on them to independently verify, and then breaking through to experientially understanding them by putting into application the way of practice to end suffering: the noble eightfold path. The eightfold path is gradually cultivated with gradual practice per the gradual training guidelines.

The breakthrough of experientially understanding the four noble truths happens via first understanding the four noble truths in the light of the five aggregates, the six sense bases and through dependent origination, and then training in the eightfold path. This collection of teachings can be a starting point at deeply soaking in the four noble truths: A handful of leaves 🍃 - Essential Teachings of the Buddha to Understanding The Four Noble Truths.