This is because, prior to starting the mission, he was instructed by Sejong (a Korean king) that 'You should learn how to make paper, how to make hard blades and how to build houses and should bring back the technologies concerned,' or he was instructed to introduce technologies in Japan.
これは、渡航前に世宗(朝鮮王)から「倭の紙、堅籾、造作の法また宜しく伝習すべし」と、日本の技術を導入するように命じられていたからである。