• aho — ah
  Exclamation of wonder. Gauḍīyas: even Sāndīpani — Kṛṣṇa's own guru — is in vismaya at the depth of his disciples' devotion. The guru is moved by the disciple's love.
• he putrakaḥ — O children
  Vocative — diminutive of putra (son). The guru addresses them as his sons. Gauḍīyas: the guru-śiṣya bond is parental, not contractual.
• ātmā — the body
  Here, the bodily self. Sāndīpani names the body as 'most dear to every living creature' — and then notes that his disciples disregarded it for him. Gauḍīyas note the distinction: ātmā here is body-self (sthūla-deha), not the eternal jīva-ātmā or paramātmā.
• preṣṭhaḥ — the most dear
  Superlative of priya. Most-dear. The body is universally most-dear — except in the disciple who has shifted his most-dear to the guru. Gauḍīyas: rasa-target shifts; that is the work of bhakti.
• mat - parāḥ — dedicated to me
  Compound: mat (me, the guru) + para (devoted, oriented). Mat-para is also Kṛṣṇa's epithet for His own bhaktas (BG 12). Gauḍīyas: guru-para and kṛṣṇa-para are the same orientation under two forms.

A father weeping over sons who slept outside in the rain for him — the rasa is not abstract sevā, it is bodily devotion seen and named. Sāndīpani's wonder is the chapter's quiet bhakti-theory: the disciple who disregards the body for the guru is the disciple Bhagavān honors.