In plain words
From food beings arise; from rain food is produced; rain arises from yajña, and yajña arises from action.
Word for word
From food beings come to be; from rain [is] the origin of food; from yajña comes rain; yajña is born of action.
The commentators
Bhagavadgītābhāṣyam
इतश्च अधिकृतेन कर्म कर्तव्यम् जगच्चक्रप्रवृत्तिहेतुर्हि कर्म । कथमिति उच्यते —
अन्नात् भुक्तात् लोहितरेतःपरिणतात् प्रत्यक्षं भवन्ति जायन्ते भूतानि । पर्जन्यात् वृष्टेः अन्नस्य सम्भवः अन्नसम्भवः । यज्ञात् भवति पर्जन्यः, ‘अग्नौ प्रास्ताहुतिः सम्यगादित्यमुपतिष्ठते । आदित्याज्जायते वृष्टिर्वृष्टेरन्नं ततः प्रजाः’(मनु. ३ । ७६) इति स्मृतेः । यज्ञः अपूर्वम् । स च यज्ञः कर्मसमुद्भवः ऋत्विग्यजमानयोश्च व्यापारः कर्म, तत् समुद्भवः यस्य यज्ञस्य अपूर्वस्य स यज्ञः कर्मसमुद्भवः ॥ १४ ॥
In plain words
And here is another reason action must be performed by anyone qualified for it: action itself is what keeps the wheel of the world turning. How does that work? Kṛṣṇa is about to explain —
Beings are born directly from food — food that has been eaten and turned into blood and seed. Food, in turn, arises from rain, and rain arises from sacrifice. This is exactly what the smṛti tells us: 'the oblation, duly cast into the fire, reaches the sun; from the sun rain is born; from rain, food; and from food, creatures' (Manusmṛti 3.76). Here 'sacrifice' actually means the apūrva, the unseen merit sacrifice produces. And that very apūrva 'arises from action' — meaning the ritual activity of the priest and the one who sponsors the sacrifice is what we call 'action' here; and it is this action that gives rise to the sacrifice, to the apūrva. That is what it means for sacrifice to have 'arisen from action'.
Close to the Sanskrit
And for this reason too, action is to be performed by the one who is qualified [for it]: action, indeed, [is] the cause of the functioning of the wheel of the world. How [so]? — it is [now] being stated —
From food — [i.e.] eaten [food], transformed into blood and semen — directly, beings come into being, are born. From the rain-cloud — [i.e.] from rain — [there is] the arising of food; [that is] 'the arising of food'. From sacrifice, the rain-cloud comes into being: 'the oblation duly cast into the fire reaches the sun; from the sun, rain is born; from rain, food; from that, creatures' (Manusmṛti 3.76) — because of this smṛti [statement]. 'Sacrifice' [means] the apūrva. And that sacrifice [i.e. the apūrva] [is] 'arisen from action' — [i.e.] the activity of the officiating priest and the sacrificer [is called] 'action'; that [action is] the source of which sacrifice, [i.e.] of the apūrva — that sacrifice [is] 'arisen from action'.