Two important points to make in this short article:
1. jhana and samadhi both often use a metaphor of a fire. Based on passages like this, 'jhana' being a fire that burns away defilements seems to be what the Buddha intended, and not just a fanciful commentary explanation as I originally thought.
2. the Buddha expects his disciples to be in jhana and samadhi all the time. Several passages in the EBT, such as this one, make that point explicitly. 'nicca' = permanent, constant. Noble silence means second jhana, and 'pleasant abiding' (dittha dhamma sukha vihara) is a code phrase for 3rd jhana.
2b. always in jhana and samadhi means all postures, all activities, not just formal sitting practice.
excerpt from SN 7.9SN 7 all suttas
- SN 7 1. The Perfected Ones 1. Arahantavagga
Atha kho sundarikabhāradvājo brāhmaṇo saṃviggo lomahaṭṭhajāto yena bhagavā tenupasaṅkami; upasaṅkamitvā ekamantaṃ aṭṭhāsi.
|Then Sundarika the brahmin, shocked and awestruck, went up to the Buddha, and stood to one side.|
Ekamantaṃ ṭhitaṃ kho sundarikabhāradvājaṃ brāhmaṇaṃ bhagavā gāthāhi ajjhabhāsi:
|The Buddha addressed him in verse:|
“Mā brāhmaṇa dāru samādahāno,
|“When you’re kindling the wood, brahmin,|
Suddhiṃ amaññi bahiddhā hi etaṃ;
|don’t imagine this is purity, for it’s just an external.|
Na hi tena suddhiṃ kusalā vadanti,
|Experts say that those who wish for purity|
Yo bāhirena parisuddhimicche.
|through externals will not find it.|
Hitvā ahaṃ brāhmaṇa dārudāhaṃ,
|I’ve given up kindling firewood, brahmin,|
|now I just light the inner flame.|
|Always blazing, always undistractify-&-lucidifyd,|
Arahaṃ ahaṃ brahmacariyaṃ carāmi.
|I am a perfected one living the spiritual life.|
Māno hi te brāhmaṇa khāribhāro,
|Conceit, brahmin, is the burden of your possessions,|
Kodho dhumo bhasmani mosavajjaṃ;
|anger your smoke, and lies your ashes.|
Jivhā sujā hadayaṃ jotiṭhānaṃ,
|The tongue is the ladle and the heart the fire altar;|
Attā sudanto purisassa joti.
|a well-tamed self is a person’s light.|