My two questions are related to "slid out" and "prophetic metaphor".

Patrice opened the minivan's sliding door and the large ceramic plate that had held the bagels she took to church slid out. In a moment that was hard not to take as a prophetic metaphor, it shattered on the driveway.

I checked slide out and it means that something to slip or glide , but what is the meaning here - I guess is used like a noun? 
Second question prophetic metaphor I checked and it is hard to understand why those two words are used in this case and why not that was not hard to instead of that was hard not to take ...

I am curious.