। ॥
In plain words
While the body is taken for the Self, the enquiry 'He am I' helps the search for the Supreme. When oneness with one's own Self is attained it serves no purpose, just as a man has no need to prove to himself that he is a man.
Word for word
The enquiry 'He am I', while the body is taken for the Self, gives help to the search for the Supreme. Once oneness with one's own Self is attained, it then serves no purpose, as the proving of manhood for a man.