The Book of Songs, also known as the Shijing, is a collection of ancient Chinese poetry that is one of the "Five Classics" of Confucianism. The reason there are only poems in the Book of Songs is due to its origins as a collection of folk songs from the Western Zhou Dynasty (1046–771 BCE). These songs were composed by various authors and were meant to convey a range of emotions, social values, and historical events. The poems were initially intended for performance and were part of the oral tradition before being written down.

The Book of Songs primarily consists of poems because it was compiled to preserve the cultural and historical heritage of the time. The songs were used for various purposes, including rituals, entertainment, and political expression. The poetic form allowed for the concise expression of complex ideas and emotions, making it an ideal medium for these purposes. Additionally, the poetic structure facilitated the memorization and transmission of the songs across generations.

Data from the Book of Songs itself provides insight into its poetic nature. The collection contains 305 poems, which are divided into three categories: wind songs (feng), earth songs (yi), and shi. The wind songs are believed to have originated from the central plains of China, while the earth songs are thought to have come from the states surrounding the central plains. The shi category includes poems from various regions and is considered to be the most sophisticated in terms of language and style.

The poetic structure of the Book of Songs is characterized by its use of repetitive phrases, parallelism, and a consistent meter. These features contribute to the musicality and memorability of the poems. For example, many of the songs use a repetitive refrain, which was likely sung by the chorus during performances. This repetition not only reinforces the message of the poem but also creates a sense of unity and continuity.

Furthermore, the Book of Songs reflects the social and political context of its time. The poems often address themes such as love, loyalty, power, and justice. They provide a window into the lives and values of the people during the Western Zhou Dynasty. The poetic form allowed the authors to convey these themes in a way that was both engaging and thought-provoking.

In conclusion, the Book of Songs is a collection of poems because it was originally a compilation of folk songs that served various cultural and social purposes. The poetic form was well-suited for the transmission of complex ideas and emotions, and it provided a means for the expression of social and political values. The data from the Book of Songs itself supports this analysis, as the collection is characterized by its musicality, repetitive structure, and thematic content.