For just one example, Baptists do not believe in infant Baptism. Lutherans do. Both read the same Bible and claim to be led by the same Holy Spirit in their
personal interpretation of that same Bible. Yet, both cannot be right. One position is contradictory to the other. And there are many other similar doctrines within Protestantism, all based on someone’s personal interpretation of Scripture. St. Peter disagrees with that approach. See 2 Peter 1:20.
Really, it is quite irrelevent to a Lutheran what Baptists think. We would consider their teaching on Baptism as heterodox, as it is not in keeping with scripture, the confessions, or even the universal Church.
Additionally, and similarly, Catholics teach Purgatory, Orthodox do not. Both claim to be the one true Church, teaching from Sacred Tradition and Sacred Scripture. :Yet, both cannot be right. One position is contradictory to the other." And there are many similar doctrines, all based on each Church’s interpertation of Sacred Tradition and Sacred Scripture. And St. Peter disagrees with this approach, too.
I am reminded of Gal. 1:8, that says, “But even if we or an angel from heaven should preach (to you) a gospel other than the one that we preached to you, let that one be accursed!”
How can you determine that everyone but yourself is preaching a different gospel?
A great question, and one we must all, regardless of communion, must face if we are to conform to Christ’s call that “all may be one”.