The 6 are making a Stage for Serenade. Twilight was trying to get Celestia, Luna and Cadance to use their magic to make a light show, but they believed Twilight could do it.

Rarity: “It looks wretched enough already.”

Rainbow Dash: “Oh, come on, it’s fine.”

Rarity: “If you were raised in a barn! No offense, Applejack.”

Applejack: “None taken. ‘Specially since I wasn’t raised in a barn. My family just happens to have a barn, where I was born and lived in for my formative years..”