What's the use of pairing in ancient times?

Duijie, commonly known as Duijie, is the most widely used, vital, refined and economical literature and art of China culture in social life. Couplets, also known as couplets, are an art form with national characteristics that China people love to see and hear, and are the perfect combination of language art, calligraphy art and decorative art..

Dui is a folk custom name for couplets. Couplets are also related to metrical poems, emphasizing duality. The third and fourth sentences, the fifth and sixth sentences are similar to two couplets. Therefore, couplets are known as "poems among poems", which are wonderful works in China's language and literature and treasures in China's traditional culture.