In plain words
I give heat; I withhold and release the rain. I am immortality and also death; I am being and non-being, Arjuna.
Word for word
I give heat; I withhold and release the rain; and immortality indeed and death, being and non-being [am] I, O Arjuna.
The commentators
Bhagavadgītābhāṣyam
किञ्च —
तपामि अहम् आदित्यो भूत्वा कैश्चित् रश्मिभिः उल्बणैः । अहं वर्षं कैश्चित् रश्मिभिः उत्सृजामि । उत्सृज्य पुनः निगृह्णामि कैश्चित् रश्मिभिः अष्टभिः मासैः पुनः उत्सृजामि प्रावृषि । अमृतं चैव देवानाम् , मृत्युश्च मर्त्यानाम् । सत् यस्य यत् सम्बन्धितया विद्यमानं तत् , तद्विपरीतम् असच्च एव अहम् अर्जुन । न पुनः अत्यन्तमेव असत् भगवान् , स्वयं कार्यकारणे वा सदसती ये पूर्वोक्तैः निवृत्तिप्रकारैः एकत्वपृथक्त्वादिविज्ञानैः यज्ञैः मां पूजयन्तः उपासते ज्ञानविदः, ते यथाविज्ञानं मामेव प्राप्नुवन्ति ॥ १९ ॥
In plain words
And there is still more —
I become the sun and pour down heat through fierce rays. I release the rain through certain rays. And having released it, I hold it back again for eight months through other rays — then, in the rainy season, I release it once more. I am the very immortality the gods enjoy, and I am the death that comes for mortals. Sat — 'being' — is whatever truly exists in relation to what it is; and its opposite, asat, 'non-being' — that too, Arjuna, I am. But don't mistake this: it doesn't mean the Lord himself is simply nonexistent. It means effect and cause stand to each other exactly as the existent stands to the non-existent. And those who worship Me — through the paths already described, through the understanding of oneness, of difference, whatever form their sacrifice takes — those who truly know, reach exactly Me, each according to how they understood.
Close to the Sanskrit
Moreover —
I give forth heat, having become the sun, by certain intense rays. I release rain by certain rays. Having released it, again I withhold it by certain rays, for eight months; again I release it in the rainy season. I am indeed the immortality of the gods, and the death of mortal beings. Sat [is] that which exists in relation to whatever it is; the opposite of that, [namely] asat, I indeed am as well, O Arjuna. However, [this does] not [mean that] the Blessed Lord himself [is] absolutely non-existent; rather, effect and cause are, respectively, existent and non-existent. Those who, by the previously described modes leading to cessation [of rebirth] — [that is,] by the understandings beginning with oneness and difference — worship Me with such sacrifices, [being] knowers of knowledge, they attain Me alone, according to their [particular] understanding.