You do not know on what day your Lord will come.
“No one knows about that day or hour, not even the angels in heaven, nor the Son, but only the Father … So you must be ready, because the Son of Man will come at an hour when you do not expect him” (Matt. 24:36, 44).
Jesus is coming; that is certain. Nobody knows when; that is equally certain.
We’re nesting here in a short snippet of time. The Bible pictures earthly life as a mist that appears briefly and then vanishes; a fleeting shadow; a passing breeze; grass that withers and flowers that fall.
There will be only one living generation when he returns, but every generation should live in a could-be-any-moment mode. “Keep watch, because you do not know on what day your Lord will come.”
The fact of his return is certain;
the when of his return isn’t.