פירוש על בראשית 29:25

ויהי בבקר והנה הוא לאה AND IT CAME TO PASS, THAT IN THE MORNING, BEHOLD, IT WAS LEAH —But at night it was not Leah (i. e. he failed to recognise that it was Leah) because Jacob had given Rachel certain secret signs by which they could at all times recognise one another, and when Rachel saw that they were about to bring Leah to him for the marriage ceremony, she thought, “My sister may now be put to shame”, and she therefore readily transmitted these signs to her (Megillah 13b).

והנה היא לאה, whenever something had not been known or recognised previously the word הנה alerts the reader to this fact. (compare Genesis 41,7 והנה חלום, “it was a dream.”) Until Pharaoh awoke he had taken what he saw in the dream as being real.

ויהי בבוקר. When morning came, etc. The reason the Torah uses the word ויהי which always relates to some painful experience is simply that Jacob experienced anguish that Rachel had been denied him.