"That's beautiful," said Annie. Jack smiled. He agreed.
Brother Patrick turned to them. "it is such sights as this that inspire our book-making," he said.
what function is "as this" in this sentence?
It is a generalizing construction. The meaning is
It is this sight, and others quite similar to this one, that …
Obviously, it is far more concise to say
It is such sights as this that …
My feeling is that
It is sights such as this that …
is more common in American speech.