§817

In fact, "in this one and only Church of God from its very beginnings there arose certain rifts, which the Apostle strongly censures as damnable. But in subsequent centuries much more serious dissensions appeared and large communities became separated from full communion with the Catholic Church - for which, often enough, men of both sides were to blame." The ruptures that wound the unity of Christ's Body - here we must distinguish heresy, apostasy, and schism - do not occur without human sin:

Where there are sins, there are also divisions, schisms, heresies, and disputes. Where there is virtue, however, there also are harmony and unity, from which arise the one heart and one soul of all believers.