The language of poetry is the most refined, and the richest thoughts and feelings should be expressed with the least words. In ordinary words, saying less may not be able to express meaning; If you talk too much, you may be in trouble Besides, the number of words in poetry is limited, so I can't say more. If you use allusions, you can use well-known materials to make readers associate with them, which can save language and extract them.
Poetry "can't be as straightforward as prose", it should be implicit, and it should "contain infinite meaning and can be seen outside words." Good allusions can do this.
The language of poetry should be concrete, vivid and less abstract. Allusions are mostly the deeds of the ancients, often specific people or things, which can avoid abstract concepts.
The use of allusions is a matter of words. When combining words into sentences to express thoughts and feelings, sometimes words are not used directly, but the deeds or languages of the ancients recorded in ancient books are used to remind readers of these materials, so as to realize the thoughts and feelings that the author wants to express. This is the allusion.