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

Having last month considered in gāthās the length of time Śākyamuni became the Buddha, we consider in gāthās the pure world of the Buddha.

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.

See The Pure Land Where the Practicer of Lotus Sūtra Resides