Consider caterpillars and butterflies:
It would take no faith whatsoever for a caterpillar to be changed into a butterfly. It's simply a natural process.
However, if no caterpillar ever had seen another caterpillar "die" and "rise again" as a butterfly (recognizing it for what it was), it would take GREAT faith for that caterpillar to believe she literally, actually could become a butterfly. A butterfly could say to her:
"I used to look like you. I lived as one of you. Look at me now. You can become like me and live as I live - and all you have to do is what I tell you must be done to live long enough to experience the metamorphosis" -
and it would take "abiding" faith (faith that lasts despite and through "things not seen") to believe the butterfly.
The words of Jesus during his ministry constituted, at the most basic level, his promise of what could be - while his words after his resurrection and the words of his early disciples and apostles constituted their testimony of what had been for Jesus and may be for us. Their admonitions and pronouncements about what we have to do constitute the directions of our own "eternal manual" (what will produce the promised metamorphosis) - and they boil down to one simple (but not easy) statement:
"Have hope in the "substance" of what I've taught, and use my life and teachings as the "evidence" of the things that can't be seen."
In other words:
"Have abiding faith that I can make the impossible come true - and trust me enough to do what I tell you must be done, even though you are naturally inclined to believe it can't have any merit or effect."