In plain words
This same multitude of beings comes forth again and again and dissolves helplessly at the coming of night, Partha, arising again at the coming of day.
Word for word
This very host of beings, having come into being again and again, dissolves at the coming of night, helpless, O son of Pṛthā; it comes forth at the coming of day.
भूतग्रामः स एवायं भूत्वा भूत्वा प्रलीयतेरात्र्यागमेऽवशः पार्थ प्रभवत्यहरागमे
Other commentaries
The commentators
▸Bhagavadgītābhāṣyam
अकृताभ्यागमकृतविप्रणाशदोषपरिहारार्थम् , बन्धमोक्षशास्त्रप्रवृत्तिसाफल्यप्रदर्शनार्थम् अविद्यादिक्लेशमूलकर्माशयवशाच्च अवशः भूतग्रामः भूत्वा भूत्वा प्रलीयते इत्यतः संसारे वैराग्यप्रदर्शनार्थं च इदमाह —
भूतग्रामः भूतसमुदायः स्थावरजङ्गमलक्षणः यः पूर्वस्मिन् कल्पे आसीत् स एव अयं नान्यः । भूत्वा भूत्वा अहरागमे, प्रलीयते पुनः पुनः रात्र्यागमे अह्नः क्षये अवशः अस्वतन्त्र एव, हे पार्थ, प्रभवति जायते अवश एव अहरागमे ॥ १९ ॥
In plain words
To rule out the absurdity of anyone reaping what they never sowed, or losing what they rightly earned; to show that scripture's whole teaching on bondage and liberation actually accomplishes something real; and because, driven helplessly by the residue of past action rooted in ignorance, every being keeps coming into existence and dissolving, over and over, powerless to stop it — and so, to make clear why one should feel real dispassion toward this whole cycle, he now says the following —
"The host of beings" means the whole aggregate of beings, the still and the moving together. And the host that existed in the previous kalpa is this very same host — not a different one. Coming to be, coming to be, at the break of day; and again and again it dissolves when night arrives, when the day runs out — helpless, meaning it has no independence of its own in the matter. And so, Arjuna, it comes forth — it is born — just as helpless, when day breaks again.
Close to the Sanskrit
For the sake of avoiding the fault of the unearned occurring or the earned being lost; for the sake of showing the fruitfulness of scripture's teaching on bondage and liberation; and because, driven by the residue of action rooted in ignorance and other afflictions, the mass of beings, powerless, comes into being and dissolves again and again — therefore, for the sake of showing dispassion toward transmigratory existence as well, he says this —
The host of beings — that is, the aggregate of beings, characterized by the stationary and the moving — which existed in the previous kalpa, that very one is this one, not another. Having come to be, having come to be, at the arrival of day; it dissolves again and again at the arrival of night, that is, at the ending of the day, helpless, that is, not self-dependent indeed; O Pārtha, it comes forth, that is, is born, helpless indeed, at the arrival of day.