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

So I’d like to just reprint the whole thing. Forced to forgo that, I’d start by pointing out the Buddha’s repeated warning:

Thereupon the Buddha said to the great multitude including Bodhisattvas and others, “Good men! Understand my sincere and infallible words by faith!”

He said to the great multitude again, “Understand my sincere and infallible words by faith!”

He said to them once again, “Understand my sincere and infallible words by faith!”

Is there any other way to believe than by faith?

“Listen to me attentively! I will tell you about my hidden core and supernatural powers. The gods, men and asuras in the world think that I, Śākyamuni Buddha, left the palace of the Śākyas, sat at the place of enlightenment not far from the City of Gayā, and attained Anuttara-samyak-saṃbodhi [forty and odd years ago]. To tell the truth, good men, it is many hundreds of thousands of billions of nayutas of kalpas since I became the Buddha.”

Continuing . . .

All this time I have been living in this Sahā-World, and teaching [the living beings of this world] by expounding the Dharma to them. I also have been leading and benefiting the living beings of one hundred thousand billion nayuta asaṃkhya worlds outside this world.

The reality of the Triple World:

All that I say is true, not false, because I see the triple world as it is. I see that the triple world is the world in which the living beings have neither birth nor death, that is to say, do not appear or disappear, that it is the world in which I do not appear or from which I do not disappear, that it is not real or unreal, and that it is not as it seems or as it does not seem. I do not see the triple world in the same way as [the living beings of] the triple world do. I see all this clearly and infallibly. The living beings are various in their natures, desires, deeds, thoughts and opinions. Therefore, I expounded the dharma with various stories of previous lives, with various parables, similes and discourses, in order to cause all living beings to plant the roots of good. I have never stopped doing what I should do. As I said before, it is very long since I became the Buddha. The duration of my life is innumerable, asaṃkhya kalpas. I am always here. I shall never pass away.

And in gāthās:

I know who is practicing the Way and who is not.
Therefore I expound various teachings
To all living beings
According to their capacities.

I am always thinking:
“How shall I cause all living beings
To enter into the unsurpassed
Way And quickly become Buddhas?

Day 20 completes Chapter 15, The Appearance of Bodhisattvas from Underground.

Something about the shocked reaction of Maitreya and the other Bodhisattvas to the appearance of the horde that rises from the ground and struts around as though they are great pals of the Buddha just tickles me.

We have never seen
These many thousands of billions
Of Bodhisattvas.
Tell me, Most Honorable Biped!
Where did they come from?

They have gigantic bodies,
Great supernatural powers, and inconceivable wisdom.
They are resolute in mind.
They have a great power of patience.
All living beings are glad to see them.
Where did they come from?

And better still is the reaction after Śākyamuni explains:

“Now I will tell all of you in this great multitude, Ajita! [I know that] you have never seen these great, innumerable, asaṃkhya Bodhisattva-mahāsattvas who sprang up from underground. After I attained Anuttara-samyak-saṃbodhi in this Sahā-World, I taught these Bodhisattvas, led them, trained them, and caused them to aspire for enlightenment.”

Continuing …

My words are true.
Believe me with all your hearts!
I have been teaching them
Since the remotest past.

Thereupon Maitreya Bodhisattva-mahāsattva and the innumerable Bodhisattvas in the congregation doubted the Buddha’s words which they had never heard before. They thought:

‘How did the World-Honored One teach these great, innumerable, asaṃkhya Bodhisattvas, and qualify them to attain Anuttara-samyak-saṃbodhi in such a short time?’

Continuing …

“World-Honored One! It is difficult for anyone in the world to believe this. It is as difficult as to believe a handsome, black-haired man twenty-five years old who points to men a hundred years old and says, ‘They are my sons,’ or as to believe men a hundred years old who point to a young man and say, ‘This is our father. He brought us up.’ You are like the young man. It is not long since you attained enlightenment. But it is many thousands of billions of kalpas since the great multitude of these Bodhisattvas began to practice the Way strenuously in order to attain the enlightenment of the Buddha.”

Despite Maitreya’s protestation, I think he’s in need of reassurance as much as everyone:

We do not doubt your words
Because we heard them direct from you.
Explain all this so that the living beings in the future
May be able to understand your words, Buddha!

Those who doubt this sūtra
And do not believe it
Will fall into the evil regions.
Explain all this to us now!

How did you teach these innumerable Bodhisattvas
In such a short time,
And cause them to aspire for enlightenment
And not falter in seeking enlightenment?

Day 19 concludes Chapter 14, Peaceful Practices, and introduces Chapter 15, The Appearance of Bodhisattvas from Underground

The loving-kindness of Bodhisattvas:

A Bodhisattva-mahāsattva who keeps this Sūtra of the Lotus Flower of the Wonderful Dharma in the latter days after [my extinction] when the teachings are about to be destroyed, should have great loving-kindness towards laymen and monks, and great compassion towards those who are not Bodhisattvas. He should think: ‘They do not know that the Tathāgata expounded expedient teachings according to the capacities of all living beings. They do not hear, know or notice it, or ask a question about it or believe or understand it. Although they do not ask a question about this sūtra, or believe or understand it, I will lead them and cause them, wherever they may be, to understand the Dharma by my supernatural powers and by the power of my wisdom when I attain Anuttara-samyak-saṃbodhi.’

Mañjuśrī! A Bodhisattva-mahāsattva who performs this fourth set of [peaceful] practices after my extinction, will be able to expound the Dharma flawlessly.

The difficulty:

Mañjuśrī! It is difficult to hear even the title of this Sūtra of the Lotus Flower of the Wonderful Dharma [even if you try to do so, walking about] innumerable worlds. Needless to say, it is more difficult to see, keep, read and recite this sūtra.

The reward for the good fight:

The people were under the pressure
Of various sufferings.
They were fighting with the Māras
In order to emancipate themselves
From suffering.
Because I saw all this,
I expounded various teachings to them.
I expounded many sūtras with skillful expedients.

Now I know that they can understand the Sūtra
Of the Lotus Flower of the Wonderful Dharma.
Therefore, I expound it to them lastly
Just as the king took the brilliant gem
Out of his top-knot
And gave it [to the bravest man lastly].

This is the most honorable sūtra.
It is superior to all the other sūtras.
I kept it [in secret]
And refrained from expounding it.
Now is the time to do so.
Therefore, I expound it to you now.

And the benefits:

Anyone who expounds
This supreme teaching
In the evil world after [my extinction]
Will obtain great benefits as previously stated.

And yet not everyone is invited to come to the Sahā-World and preach. Bodhisattvas who had come from other worlds to hear the Lotus Sutra said:

“World-Honored One! If you permit us to protect, keep, read, recite and copy this sūtra, and make offerings to it strenuously in this Sahā-World after your extinction, we will [do so, and] expound it in this world.”

Thereupon the Buddha said to those Bodhisattva-mahāsattvas:

“No, good men! I do not want you to protect or keep this sūtra because there are Bodhisattva-mahāsattvas sixty thousand times as many as the sands of the River Ganges in this Sahā-World. They are each accompanied by attendants also numbering sixty thousand times as many as the sands of the River Ganges. They will protect, keep, read, recite and expound this sūtra after my extinction.”

The solicitude of the practiced Bodhisattvas from Underground:

Those Bodhisattvas had four leaders: 1. Superior-Practice, 2. Limitless-Practice, 3. Pure-Practice, and 4. Steadily-Established-Practice. These four [great] Bodhisattvas were the highest leaders [of those Bodhisattvas]. In the presence of the great multitude, they joined their hands together towards Śākyamuni Buddha, looked up at him, and inquired after him saying:

“World-Honored One! Are you in good health? Are you peaceful or not? Are the living beings, whom you are to save, ready to receive your teachings or not? Do they not fatigue you?’

Thereupon the four great Bodhisattvas sang in gāthās:

World-Honored One, are you peaceful?
Are you in good health?
Are you not tired
With teaching the living beings?
Are they ready
To receive your teaching,
Or are they not?
Do they not fatigue you?

Day 18 concludes Chapter 13, Encouragement for Keeping This Sutra, and begins Chapter 14, Peaceful Practices.

Chapter 13, which opened with Mahā-Prajāpatī Bhikṣuṇī, the sister of the mother of the Buddha, and Yaśodharā Bhikṣuṇī, the mother of Rāhula, being assured future buddhahood, concludes with eighty billion nayuta Bodhisattva-mahāsattvas saying:

“If the World-Honored One commands us to keep and expound this sūtra, we will expound the Dharma just as the Buddha teaches.”

They also thought, “The Buddha keeps silence. He does not command us. What shall we do?”

In order to follow the wish of the Buddha respectfully, and also to fulfill their original vow, they vowed to the Buddha with a loud voice like the roar of a lion:

“World-Honored One! After your extinction, we will go to any place [not only of this Sahā-World but also] of the worlds of the ten quarters, as often as required, and cause all living beings to copy, keep, read and recite this sūtra, to expound the meanings of it, to act according to the Dharma, and to memorize this sūtra correctly. We shall be able to do all this only by your powers. World-Honored One! Protect us from afar even when you are in another world!”

In Chapter 14, Mañjuśrī asks, “How should an [ordinary] Bodhisattva-mahāsattva expound this sūtra in the evil world after [your extinction]?”

To which the Buddha replies:

What are the proper practices the Bodhisattva-mahāsattva should perform? He should be patient, mild and meek. He should not be rash, timorous, or attached to anything. He should see things as they are. He should not be attached to his non-attachment to anything. Nor should he be attached to his seeing things as they are. These are the proper practices the Bodhisattva-mahāsattva should perform.

And:

“The Bodhisattva-mahāsattva also should know the following truth. All things are insubstantial. They are as they are. Things are not perverted. They do not move. They do not go. They do not turn. They have nothing substantial just as the sky has not. They are inexplicable. They are not born. They do not appear. They do not rise. They are nameless. They are formless. They have no property. They are immeasurable and limitless. They have no obstacle or hindrance. He should see all this. Things can exist only by dependent origination. Only perverted people say, ‘Things are permanent and pleasant.’ This truth is the second thing he should approach.”

And:

“A Bodhisattva-mahāsattva who wishes to expound this sūtra in the age of the decline of the teachings after my extinction should perform the following peaceful practices. When he expounds or reads this sūtra, he should not point out the faults of other persons or sūtras. He should not despise other teachers of the Dharma. He should not speak of the good points or bad points or the merits or demerits of others. He should not mention Śrāvakas by name when he blames them. Nor should he do so when he praises them. He should not have hostile feelings against them or dislike them. He should have this peace of mind so that he may not act against the wishes of the hearers. When he is asked questions, he should not answer by the teachings of the Lesser Vehicle, but expound the Dharma only by the teachings of the Great Vehicle so that the questioners may be able to obtain the knowledge of the equality and differences of all things.”

And:

“Again, Mañjuśrī! A Bodhisattva-mahāsattva who wishes to keep, read and recite this sūtra in the latter days after [my extinction] when the teachings are about to be destroyed, should not nurse jealousy against others, or flatter or deceive them. He should not despise those who study the Way to Buddhahood in any way. He should not speak ill of them or try to point out their faults.”

And finally in gāthās:

Anyone who wishes to expound this sūtra
Should give up jealousy, anger, arrogance,
Flattery, deception and dishonesty.
He should always be upright.

He should not despise others,
Or have fruitless disputes about the teachings.
He should not perplex others by saying to them:
“You will not be able to attain Buddhahood.”

Any son of mine who expounds the Dharma
Should be gentle, patient and compassionate
Towards all living beings.
He should not be lazy.