what are the keys to the kingdom and how are they to be used?
'"I will give you the keys of the kingdom of heaven; whatever you bind on earth will be [what is] bound in heaven, and whatever you loose on earth will be [what is] loosed in heaven."' Mt 16:19
The phrase 'the keys to the kingdom of heaven' refers to divine rule in the life of every saint. The 'binding' and 'loosing' referred to was common description of the practice of rabbis in Judea, each of whom taught his own interpretation of Scripture, one of them 'binding' a moral action that another would 'loose'. Jesus was here saying that his disciples would no longer rely on the confused and unreliable teaching of mere men, but would, by the indwelling of the Holy Spirit, possess the teaching of heaven itself. He was referring to his own divine and cosmic role, not to the importance of a mere human.
The confession made by Simon Bar-Jonah, that Jesus was the Messiah, the Christ, was and is the pre-requisite for this indwelling. Conversion is impossible without it.
But the words must be fully understood. Simon got the form of words right, and little besides. He quickly denied that Jesus was the Messiah when he attempted to dissuade Jesus from going to Jerusalem and its danger, which showed that he did not yet really understand who Jesus was; and that this incomprehension was his own fault. For that, he was described as 'Satan'.