Protestants: how do you explain the first 1500 years of Christianity?

It seems that God sent His Son into the world, Who established His Church, suffered and died for our sins, rose from the dead, ascended into Heaven, and then sent His Holy Spirit to guide us so that we might be one, as the Father and Son are one. If the Church erred for 1500 years, only to have the truth re-discovered in the Reformation, doesn't it seem like the whole life, pion, death, resurrection and Pentecost was an exercise in futility for 1500 years?