[7] Beginning in 1994, he worked as a spiritual director and professor at the Catholic University of Daejeon; he became its president from 1998 to 2003.

[8][9] On 9 July 2003, Pope John Paul II named him Bishop Coadjutor of the Diocese of Daejeon.

He expressed hope for peace on the Korean peninsula; he imagined an eventual papal visit to North Korea, but warned that it would require extensive preparations, "starting with the issue of religious freedom and the presence of priests".

[8] On 11 June 2021, Pope Francis appointed him to succeed Cardinal Beniamino Stella as prefect of the Congregation for the Clergy, with the date on which he takes office left unspecified.

[24] In February 2022, he participated in the San Damaso Ecclesiastical University of Madrid, Spain, with a conference in the fifth edition of the pastoral update sessions for priests.

[26] On 27 August, Pope Francis made him a cardinal deacon,[27] assigning him the deaconry Gesù Buon Pastore alla Montagnola.