Back in February I mentioned this construction, putting two verbs together, especially “is.” Here’s another example:
“What this spring is is a miracle,” said Sean Milanovich, 49, a member of the Agua Caliente band of the Cahuilla tribe, which makes its home in the Old Woman Mountains southeast of the spring.
https://www.washingtonpost.com/national/a-massive-aquifer-lies-beneath-the-mojave-desert-could-it-help-solve-californias-water-problem/2019/03/03/a5d8fe14-354e-11e9-af5b-b51b7ff322e9_story.html
As I mentioned last time, this looks as if it ought to be wrong somehow, but it’s not!
The first “is” goes with what’s before it, which is a noun clause. That clause functions as the subject of the second “is,” which is the sentence’s main verb.
You could reword the sentnce to make this a little easier to see:
This spring is what is a miracle.
or even:
This spring is a miracle.
Simpler, more concise. I like it.