[gbcdoj]

There's no promise for the future there

But it's explicitly stated to be a consequence of a saying that "cannot fail of its effect".

Have those Modernists introduced changes to the Catholic the faith and doctrine as it existed before they came along?

No, the Catholic faith is always the same.

[dsc]

"But it's explicitly stated to be a consequence of a saying that "cannot fail of its effect".

Look again:

"And since that saying of our lord Jesus Christ, "You are Peter, and upon this rock I will build my Church," cannot fail of its effect, the words spoken are confirmed by their consequences."

The statement that "cannot fail of its effect" is "You are Peter, and upon this rock I will build my Church."

"No, the Catholic faith is always the same."

Really? What happened to extra ecclesiam nulla salus?