Day 21 covers all of Chapter 16, The Duration of the Life of the Tathāgata.

Having last month heard Śākyamuni explain why he disappears, we learn about the pure land.

I can do all this by my supernatural powers.
I live on Mt. Sacred Eagle
And also in the other abodes
For asaṃkhya kalpas.

The [perverted] people think:
“This world is in a great fire.
The end of the kalpa [of destruction] is coming.”
In reality this world of mine is peaceful.
It is filled with gods and men.
The gardens, forests and stately buildings
Are adorned with various treasures;
The jeweled trees have many flowers and fruits;
The living beings are enjoying themselves;
And the gods are beating heavenly drums,
Making various kinds of music,
And raining mandārava-flowers on the great multitude and me.

[This] pure world of mine is indestructible.
But the [perverted] people think:
“It is full of sorrow, fear, and other sufferings.
It will soon burn away.”

Because of their evil karmas,
These sinful people will not be able
To hear even the names of the Three Treasures
During asaṃkhya kalpas.

To those who have accumulated merits,
And who are gentle and upright,
And who see me living here,
Expounding the Dharma,
I say:
“The duration of my life is immeasurable.”
To those who see me after a long time,
I say, “It is difficult to see a Buddha.”

See This Pure Land