Yes, hearing well, then singing well. This sentence doesn't mean that you will sing well if you hear well. singing well is something that have to be practiced. You also need to practice the singing techniques, start from how to breath until the way for mastering the soul of a song you will sing.

Ear is the second most important organ after voice and hearing is the first step that have to be completed before singing. So you wont sing well if you can't hear the notes well.