Protestantism, on the other hand, associates the unity of the church first of all with the oneness of the head of the church (Eph. 1:10; 5:23), with the communion of all believers through one and the same Spirit (1 Cor. 6:17,19; 12:13; 2Cor. 12:18; Eph. 4:4), with Christ and with each other (John 10:16; 15:1; Rom. 12:5; 1 Cor. 12:12-13; Eph. 1:22), and further, with the unity of faith, hope, and love, and of baptism, and so forth (Eph. 4:3-5). This unity, though primarily spiritual in character, nevertheless exists objectively and really, and it does not remain completely invisible. It manifests itself outwardly—-albeit in a very imperfect way—-and at least to some degree comes to light in that which all Christian churches have in common. No Christianity exists above or beneath religious differences, but there is indeed a Christianity present amid religious differences. Because we tend to be most aware of the differences and schisms in Christianity, we constantly run the danger of disregarding this–nevertheless truly existing–unity. That which unites all true Christians is always more than that which separates them.
~Herman Bavinck~
Reformed Dogmatics Vol. 4: Holy Spirit, Church, and New Creation (Grand Rapids, Michigan; Baker Academic; 2003) p. 321.
The Old Guys 