But rest assured, kids, that such a time did exist

[Volcano1985]

In the steady barrage of images that make up the digital age, it's almost impossible to fathom a time when photographs of people were nonexistent. But rest assured, kids, that such a time did exist -- and it really wasn't that long ago in the grand scheme of things

What do black lines mean?

 

[Munch]

What do black lines mean?

But rest assured, kids, that such a time did exist

You can believe me, young people, there was a time in the past when this was true.

in the grand scheme of things

If you look at the “big picture”, if you think about all of human history.

 

[Volcano1985]

How could you link rest assured with you can believe me ? Can you explain me please?

 

[Barb_D]

Rest assured = remain in a state of assurance of the truth = be confident that this is true = you can completely believe this to be true