The World Honored One emits light from between his brows. A Bodhisattva extols and beseeches the Buddha to speak. The Buddha emits light from his mouth. What is the meaning of this auspicious portent? Universal Worthy Bodhisattva illuminates. He expounds upon the inconceivabilities and manifestations of the Thus Come One. The Sutra says,
When the sun first comes up
It shines first on the high mountains, then the others,
Then  shines on the high plains, then the whole land,
            yet the sun never has any discrimination.
The light of the Buddha is also thus.
First illumining the Bodhisattvas, then the self-enlightened,
Then last the Sound Hearers and all living beings.
Yet the Buddha basically has no stirring thoughts.

Annotation
The Buddha’s Teaching can be divided into Five Periods:

1. The Avatamsaka Period - This teaching is compared to whole milk. It is like the sun, which upon rising first illumines the tall mountain. It is analogous to the flavor of milk because milk means,
2. Beginning of all flavors, which is analogous to the direct Teachings of the Buddha immediately upon his enlightenment. It comes first, it is the first flavor.
3. It is the beginning of all the Buddha’s Deeds.
4. It is taught at a time when the Teachings for those of inferior faculties have not been expounded.

The Avatamsaka is known as the Perfect Teaching,

1. Because it directly explains inconceivable causes and conditions.
2. Because there is total unobstructed perfect interpenetration of specifics and principles.
3. Because it teaches people of the highest faculty.

The Buddha upon attaining ultimate enlightenment, immediately spoke the Avatamsaka Sutra - That is similar to the sun which when it rises first shines on the high mountains. However, it is not that the Buddha discriminates when he dispenses the Teaching. But, rather it is like the sun which upon arising will first illumine the mountain peaks because they are the highest.
In the same way, when the Buddha speaks the Avatamsaka Sutra, those who can immediately receive the light of this Teaching are those of the highest capacities / faculties, and they are the Bodhisattvas. The sun shines on all things equally. But, those places below the mountain tops will receive the sun’s brilliant rays later - It is not the fault of the sun that some can only receive its light later. When the Buddha expounded the Avatamsaka Sutra, it is not the fault of the World Honored One if there are those who are unable to receive his Teaching right away. The fault lies in the inferior faculties of the living beings themselves. For instance, if kids from the kindergarten go into a university, they cannot understand what the Professor is teaching. But, the college students (the Bodhisattvas) will be able to understand what the Professor (Buddha) says.
The Tripitaka Master Hsuan Hua explained it in the following manner,
The newly arisen sun first shining on high mountains is just the meaning of sudden, the Sudden Teaching. The Flower Adornment Sutra was taught to transform the Great Bodhisattvas, the Great Knights of the Dharma Body, those of the Ten Dwellings, the Ten Conducts, the Ten Transferences, the Ten Grounds, and Equal Enlightenment, and those Great Bodhisattvas are similar to lofty mountains.

1. The Agama Period - This teaching is compared to coagulated milk, the flavor of cream. It refers to the Hinayana Sutras.
2. The Vaipulya Period - This teaching is compared to curdled milk, the flavor of curds. It refers to a Mahayana form of Scripture. The Shurangama Sutra is said to be taught during this period.
3. The Prajna Period - This teaching is compared to butter, the flavor of butter. It refers to world-transcending wisdom. An example is, The Great Prajna Sutra.
4. The Dharma Flower and Mahaparinirvana Period - This teaching is compared to classified butter, to the flavor of ghee. The Wonderful Dharma Lotus Flower Sutra and the Mahaparinirvana Sutra were taught during this period.

In the Prologue ( Second Door ) to the Avatamsaka Sutra by National Master Ch’ing Liang, he says,
The Avatamsaka Sutra is called The Sudden Teaching,
while all the rest are called The Gradual because,
beginning in the Deer Park
 and ending between the twin trees,
they go from Small to Great…
This Sutra, like the newly arisen sun,
first illumines lofty mountains,
which is just the meaning of Sudden.