Nikon no tokudo refers to attain Nirvana and salvation (Jodo (completing the path to becoming a Buddha by attaining enlightenment)) by listening to the chanting of Myohorenge-kyo Sutra (the Lotus Sutra).
耳根の得道（にこんのとくどう）とは、妙法蓮華経の声を聞くことによって、成仏得道（成道）すること。