In few respects [did Protestantism differ from Catholicism] more than in its establishment of the principle of an ongoing reformation. While most of the Reformers, once established, tended practically to resist extensions of reformation that would jeopardize their status and definition, almost all Protestants, at least nominally, assented to the idea that “ecclesia reformatat semper reformanda”–i.e., that the church was always reformed and always in need of further reformation. The Protestant movement, then, was conceived as an unfinished product, constantly to be judged by a reading of the Bible, its polity continually subject to debate, its policy open to ongoing appraisal and change. — “The Ongoing Reformation of the Church,” History of Protestantism entry, Encyclopedia Britannica, 1974 edition.
They trusted the Holy Spirit, whom Jesus said would return to further guide and teach each and every one of us.
As hard as the struggle can sometimes be, we can rest assured that we are, day by day and step by step, becoming a better church.