Let's talk specifically about the contribution at that time:
The contribution of the envoys to the Tang Dynasty was firstly to introduce the laws and regulations of the Tang Dynasty and promote the innovation of the Japanese social system. Tang envoys were sent to Chang 'an to study and read extensively. After returning to China, they participated in the pivot and imitated the Tang system. For example, the "Dabao Decree" was formulated according to the laws and regulations of the Tang Dynasty. It also imitated the educational system of the Tang Dynasty and set up various schools to teach Sinology and cultivate talents. In 818, according to the suggestion of sending an envoy to the Tang Dynasty, Kanehara Kikuhara, Emperor Xie changed the etiquette, and ordered that "clothes for men and women should be made in the Tang Dynasty" (Volume 123 of Great Japanese History), even the calendars, festivals and customs should be imitated as much as possible by China.
Secondly, learn from the culture of the prosperous Tang Dynasty and improve the level of Japanese culture and art.. Every time he sent envoys to the Tang Dynasty, he brought back a large number of Chinese Buddhist scriptures, and the government and the public competed to praise and write Tang poems in Chinese. Poems of famous poets in the Tang Dynasty, such as Bai Juyi, were widely circulated in Japan. The student monks studying in Tang Dynasty also created Japanese pseudonyms by using Chinese character radicals or cursive script. The envoys also imported calligraphy, painting, sculpture, music, dance and other arts from the Tang Dynasty, which were digested and transformed into Japanese national culture.
Even techniques such as Go and sports such as sumo and polo were introduced from the Tang Dynasty. Japanese painters, musicians and even Weiqi experts often visit the Tang Dynasty to learn skills and watch competitions.