Many of us must remember the time we had faith. The definition is in Hebrews11:1:

Now faith is confidence in what we hope for and assurance about what we do not see.

Some versions use the word 'evidence' instead of 'assurance'. Another word used is 'conviction'. I think they are talking about evidence from the real world that convinces them that their belief in the next world is valid. So when the scriptures talk about the wicked world, for example:

But understand this: In the last days terrible times will come. For men will be lovers of themselves, lovers of money, boastful, arrogant, abusive, disobedient to their parents, ungrateful, unholy, unloving, unforgiving, slanderous, without self-control, brutal, without love of good (2 Timothy 3:1-3)

These verses, which are true of any age, are taken as evidence that scripture is correct and so faith is exercised in the future prophecies.