‘And Laban gathered together all the men of the place and made a feast, and so it was that in the evening he took his daughter Leah and brought her to him, and he went in to her. And Laban gave Zilpah his handmaid to his daughter Leah for a handmaid.'
The wedding feast is arranged. It will last for seven days (Genesis 29:27). And it is now that we first begin to see Laban's deceitful ways, although we must be fair and recognise that he has been put in a difficult position. He had hoped that Leah might be married off, but it had not happened, and custom forbade Rachel being married first.
As he ponders the problem he sees the solution. Instead of being open and honest he foists Leah, who would be heavily veiled for the wedding, on Jacob. When they go to bed it is dark and presumably Leah kept silent. Thus Jacob does not realise until daylight that his silent and submissive companion is Leah. And by then it is too late. He is legally committed to Leah.
The mention of Zilpah is to indicate that she no longer belongs to Laban but to Leah, and thus indirectly to Jacob. She joins those whom Jacob has brought with him as a member of his ‘household'. But noteworthy is the meagreness of the gift. There is no mention of any other dowry. Laban is getting rid of his daughters on the cheap. (Rebekah was provided with a number of young women - Genesis 24:61). Jacob has come with little in the way of gifts. Laban returns the compliment.