Question

What does this mean?

"These things look like the cautious patting and petting of a spirited horse preparatory to mounting him when it is dreaded that may give the rider a fall."

Answer 1

In my opinion it's metaphorically speaking of failure. we all know that we may fail from time to time. therefore, we prepare ourselves for a possible failure. "the patting and petting of the spirited horse" refers to us preparing ourselves for failure and we are the "riders" of life that occasionally gives us "a fall

Answer 2

Lincoln uses this metaphor in order to talk about the futility of continuing to support slavery. He tells us that people who defend this position are like those who pat and pet a violent horse as they are preparing to mount it. Just like these people, who already know they are likely to fall, those who support slavery are aware that all their efforts will be pointless, as they will most likely end up failing.