• ātma - jaḥ — a son
  Literally 'self-born' — the child is the parent's own ātman extended. The compound implies that refusing parents is a kind of self-refusal, which is why the karmic recoil is sva-māṁsa-khādana.
• kalpaḥ — capable
  The condition matters: dharma applies to those with means. Kṛṣṇa is careful — He is not condemning the helpless poor but the able who choose otherwise.
• vṛttim — a livelihood
  Vṛtti = sustenance, support. The minimum a capable child owes — not luxury, but the means of living. Gauḍīya gṛhasthas like Sanātana Gosvāmī before renunciation took this baseline obligation seriously even while preparing for tyāga.
• pretya — after passing away
  After death — the karma matures post-mortem in pretaloka. Kṛṣṇa is using standard śāstric eschatology to land a domestic duty; bhakti does not abolish dharma's natural retribution.
• sva - māṁsam — his own flesh
  The visceral image is intentional. Manu-smṛti uses similar formulae; Kṛṣṇa is quoting the tradition's own iron rhetoric to make the duty inescapable. Sva-māṁsa-khādana = the karmic boomerang of consuming one's source.

A son with the means who refuses his aging parents is, in the śāstra's stark image, made to eat his own flesh hereafter — because he is already eating it now, only the chewing is invisible. Kṛṣṇa quotes the heavy verse so the dharma can land on every gṛhastha listening over the householders' shoulders.