If Christianity is both social and dogmatic, and intended for all ages, it must, humanly speaking, have an infallible expounder, else you will secure unity of form at the loss of unity of doctrine, or unity of doctrine at the loss of unity of form; you will have to choose between a comprehension of opinons and a resolution into parties; between latitudinarian and sectarian error…you must accept the whole or reject the whole…it is trifling to receive all but something which is as intergral as any other portion. Thus it would be trifling tinded to accept everythign Catholic except the head of Christ’s body on earth.
As usual, with Newman, the style is dense, yet somehow terse. He nails it.
Here’s my paraphrase: If the faith is to be applied now and in all ages, then it needs to be adaptable, and for it to be adaptable you have to have someone (or some institution) who decides when and how far the adaptions can be made. This interpreter needs to be infallible. If you don’t have this infallible authority you will argue and disagree and eventually fall into one of two errors. Latitudinarian error preserves unity of form, but sacrifices unity of doctrine. The Anglicans and other mainstream Protestant Churches are an example of this. You can believe anything as long as you don’t break down into schism.The other error is sectarian. Those who move into a sect maintain unity of doctrine, but lose unity of form. The multitude of Evangelical, independent denominations are an example of this error.
These are the only choices for non-Catholic Christians, and every individual or group falls into one camp of the other. The non-Catholic individual or group is either sectarian (and there are more and more sects as more and more divisions take place) or they are latitudinarian, and these groups (in their attempts to include everyone and allow everything) are now so far from historic Christianity that they will soon need to take a new name.
The only other option is the Catholic Church, and this is where Newman’s last few lines hit home. He speaks to all Christians who want to be ‘Catholic’ without coming into the Catholic church.