• mūḍhaḥ — the fool
  From √muh — to be deluded. Śuka's editorial label. The Bhāgavatam calls anyone mūḍha who undergoes immense effort without first asking who Bhagavān is (cf. Gītā 7.15, na māṁ duṣkṛtino mūḍhāḥ).
• paśu-patim — Śiva, the protector of animallike men
  Compound from synonyms. Paśu literally means animal — by extension the bound jīva. Prabhupāda's gloss reads paśu-pati as guardian of those still in animal consciousness: the right deity for one who wants only a weapon, not Bhagavān Himself.
• āradhayām āsa — worshiped
  Periphrastic perfect of √rādh. Same verbal root from which ārādhana and rādhā arise: the action of pleasing. Here the action is correctly performed but pointed at the wrong end — kāmya-rādhana, worship for a private wish, not nirupādhi-bhakti.
• pāṁśu — of dust
  A handful of dust per day. The Bhāgavatam's austerity-asuras choose extreme physical reduction, but the Gauḍīya reading is sharp: tapas without bhakti, however terrifying, is bhukti or mukti aimed asuric — not the road to Bhagavān.
• muṣṭim — a handful
  Accusative of muṣṭi. The same word that names the boxing-match grip of Cāṇūra and Muṣṭika in SB 10.43–44 — the asuras Kṛṣṇa killed. Even the dust Śālva clenches foreshadows the asura's clenched, fruitless effort.

• Where does my own discipline sometimes serve a purpose I haven't examined?
• What is the intention behind my most demanding practices?

Like a man who plants a tree in poisoned soil and waters it daily expecting sweet fruit, Śālva subjects himself to year-long austerity, but the goal — destruction of Kṛṣṇa's people — is the poison; no length of tapas can purify a fruit aimed at Bhagavān's devotees.