[Iscool]

One Holy Spirit, One Christ, One God the Father, One Body of Christ, One Church. That’s where the unity is.

And that's what Protestants believe...But just as we know the Assemblies of God is not the One Church, we know, as the bible teaches, the Catholic denomination is not the One Church...

[Salvation]

The Catholic Church is the One, Holy, Catholic and Apostolic Church.

These two links address the “One” aspect of those four marks of the Church.

http://www.freerepublic.com/focus/f-religion/3133474/posts?page=26#26