These wasan refer primarily to the great compassionate working of bodhisattvas in order to bring us to realisation, resulting from Amida's directing of merits for our return to this world.

15

The light is more luminous than the heavenly bodies;
Thus Amida is called “Light that Surpasses the Sun and the Moon.”
Even Sakyamuni’s praise cannot exhaust its virtues,
So take refuge in the one without equal.

True wisdom is not only inconceivable but it is infinitely brightening. This raises the questions, how if it surpasses the brightness of anything else, why can't we see it? The usual answer is that we are too attached to self-power to be able to "get over ourselves" and accept the light. There is an interesting contradiction here, since if the light really was infinitely bright, it should be unavoidably seen no matter our afflictions. This really highlights the immensity of our attachment to self-power: it is so great that we cannot even see an infinitely luminous light. Since it is infinitely luminous, Shakyamuni Buddha even spending infinite time praising it would not be able to cover do it justice!

16

When Amida, on becoming a Buddha, first taught the dharma,
The sages present were numerous beyond reckoning;
All who aspire to be born in the Pure Land,
Take refuge in Amida, of the vast assembly.

vast assembly: The sentient beings of the ten quarters will all attain Buddhahood in the land of bliss; this is the significance of dharma-body.

The near infinite number of sages present hear and spread the teaching, therefore they, like Shakyamuni, are an expression of the 17th vow, the vow that all Buddhas say the name. The note is interesting, though to me it is not clear how it is related to the wasan.

17

The countless great bodhisattvas of the land of happiness
Have reached “succession to Buddhahood after one lifetime”;
Entering the compassionate activity of Samantabhadra,
They unfailingly work to save beings in defiled worlds.

succession to Buddhahood after one lifetime: If one goes to the land of bliss, one becomes the highest disciple of Amida.
compassionate activity of Samantabhadra: We sentient beings, if we attain the land of bliss, will awaken great love and great compassion, and going throughout the ten quarters, will benefit sentient beings. The supreme, perfect compassion of Buddhas is referred to by [the name of the bodhisattva] Samantabhadra.

This describes how bodhisattvas work on us in our day to day lives, working to awake us to the truth of Other Power, through various skilful means. Because they have gone to the Pure Land, and because Amida directs his merits for our returning to this world, they are able to engage in this activity with the perfect compassionate mind. The great love and compassion referred to as the compassionate activity of Samantabhadra is none other than the mind of shinjin that we receive through Amida's directing of merits.

18

Amassing a stock of virtues from the Buddhas
For sentient beings of the ten quarters,
They bring them to entrust themselves to the universal Primal Vow;
So take refuge in Amida, the oceanlike great mind.

oceanlike great mind: Amida Buddha’s mind is vast and deep, boundless and without limit.

If you notice your own finitude, your faults, your shame, or you simply are brought to ponder on life itself, all that is the working based on the compassion of Samantabhadra, in order to bring you to entrust to the Primal Vow. In truth, bodhisattvas take on every form, because any aspect of reality can guide you towards such reflections.

Therefore, the next time you feel shame at your wrongdoings, you can immediately say "thank you, bodhisattva!"

19

Avalokitesvara and Mahasthamaprapta
Together illumine the world with the light of compassion,
Never resting even for a moment
From bringing to nirvana those with mature conditions.

Mature conditions means that the compassionate activity of bodhisattvas has worked on us for long enough that we come to realise shinjin. Those bodhisattvas never rest, but also they work effortlessly, and so they never tire either, and they don't need our support.

20

Those who reach the Pure Land of happiness
Return to this evil world of the five defilements,
Where, like the Buddha Sakyamuni,
They benefit sentient beings without limit.

This refers to Amida's directing of virtues for our return. As Mahayana Buddhists we do not have the intention of permanently leaving this world, but to come back as soon as possible to help beings out of great compassion.