On Pentecost when Peter preached the first gospel sermon this was the turning of the keys of the kindgom. This is how Peter bound and loosed sins. The sins of all who will not believe in Jesus, repent of their sins, and be baptized, were bound when Peter preached that first sermon, and the sins of all who would were loosed. Tertullian says exactly that in 210 AD when he opposed the newly forming RCC’s position on the binding and loosing:

On Modesty, Chapter 21:

If, because the Lord has said to Peter, “Upon this rock will I build My Church,” [and] “to thee have I given the keys of the heavenly kingdom;” or, “Whatsoever thou shalt have bound or loosed in earth, shall be bound or loosed in the heavens,” you therefore presume that the power of binding and loosing has derived to you, that is, to every Church akin to Peter, what sort of man are you, subverting and wholly changing the manifest intention of the Lord, conferring (as that intention did) this (gift) personally upon Peter? “On thee,” He says, “will I build My Church;” and, “I will give to thee the keys,” not to the Church; and, “Whatsoever thou shalt have loosed or bound,” not what they shall have loosed or bound. For so withal the result teaches.

In (Peter) himself the Church was reared; that is, through (Peter) himself; (Peter) himself essayed the key; you see what (key): “Men of Israel, let what I say sink into your ears: Jesus the Nazarene, a man destined by God for you,” [Acts 2:22] and so forth. (Peter) himself, therefore, was the first to unbar, in Christ’s baptism, the entrance to the heavenly kingdom, in which (kingdom) are “loosed” the sins that were beforetime “bound;” and those which have not been “loosed” are “bound,” in accordance with true salvation;

Peter turned the key and bound the sins of all who will not believe on Jesus, repent, and be baptized. And the sins of those who will are loosed. He opened and no man may shut. He shut and no man may open. Nobody else can turn the keys, not even Paul. They were Peter’s alone, and this is why it was Peter who preached the first sermon after the resurrection.  So nobody can change the requirements.  Nobody can take away belief, repentance, nor baptism.  Because only Peter has the keys—Peter himself; there are no successors to that authority, not even Paul.