[1] Yi Saek played a crucial role in the introduction and localisation of philosophy of Zhu Xi.

Aiming to solve the social problems facing Goryeo, Yi fulfilled his responsibilities as a scholar, educator and politician based on his experience studying at Guozijian, a national Chinese university.

Yi Saek played a very important role in introducing Neo-Confucianism to Goryeo, which was the theoretical background for the founding of Joseon.

[3] Many of his disciples, such as Chŏng To-jŏn and Kwŏn Kŭn, used Neo-Confucianism as the ideological basis for overthrowing the Buddhist kingdom of Goryeo and establishing Confucian Joseon.

However, Yi Saek himself remained loyal to the Goryeo Dynasty and didn't believe the wiping out of Buddhism, as Chŏng To-jŏn insisted, would be of any benefit.