Is the Catholic who confesses his sins to a priest any better off than the non-Catholic who confesses directly to God?
Yes. First, he seeks forgiveness the way Christ intended. Second, by confessing to a priest, the Catholic learns a lesson in humility, which is avoided when one confesses only through private prayer. Third, the Catholic receives sacramental graces the non-Catholic doesnˇ¦t get; through the sacrament of penance sins are forgiven and graces are obtained. Fourth, the Catholic is assured that his sins are forgiven; he does not have to rely on a subjective "feeling." Lastly, the Catholic can also obtain sound advice on avoiding sin in the future.
During his lifetime Christ sent out his followers to do his work. Just before he left this world, he gave the apostles special authority, commissioning them to make Godˇ¦s forgiveness present to all people, and the whole Christian world accepted this, until just a few centuries ago. If there is an "invention" here, it is not the sacrament of penance, but the notion that the sacramental forgiveness of sins is not to be found in the Bible or in early Christian history.