Confession of sin is definite. A fellow who is unsure whether he has sinned should find out. Until he knows and admits his sin, he can make no real confession. Confession of sin is specific. A confession of generally sinful life is proper but this is not the thing under consideration.
Confession admits the particular sin.
It is so hard that few will do it. This is common practice in civil law. The criminal is allowed to admit a misdemeanor rather than the felony he actually committed. Confession names sin. Confession addresses the one who has been sinned against.