The original sentences:
It was necessary first to arrive at that degree of sophistication where we no longer set our own belief against our neighbour's superstition. It was necessary to recognize that these institutions which are based on the same premises, let us say the supernatural, must be considered together, our own among the rest.
Is the last part as below if fully written out?
...must be considered together, [and] our own [must be considered] among the rest.
"the rest" means ours only, and it does not include those institutions sharing the same premises mentioned earlier.