B.G 9.19
I am the source of heat, and I withhold and send forth the rain. O Arjuna, know that I encompass both immortality and death, and I am simultaneously the cause and effect.
Gīta Bhāshya 9.19
In the current context 'Sat' means the effect, and 'Asat' is used to mean the cause. Same is substantiated through testimonials.
"'Sat' is the effect; 'Asat' is the cause. Because the manifest is of the nature of expression, the cause too is denoted by the term."
- Thus indeed is the declaration.
"That which is the universe, composed of both the unmanifest and manifest, is beyond both cause and effect."
- stated thus in the Mahābhārata as well.
Gīta Tātparya 9.19
Due to the completeness of virtuous qualities, supreme Lord Vishnu is called 'sat'. As no one else is superior in qualities to Lord Vishnu, i.e. He is beyond ordinary qualities. Hence he is spoken of as 'asat'.
"Due to the completeness of virtuous qualities, supreme Lord Vishnu is called 'sat'; no one else is superior in qualities to Lord Vishnu, i.e. He is beyond ordinary qualities, hence he is spoken as 'asat'."
- stated thus in the śabdanirṇaya, a book on the determination of words.
