Questions for Kierdegaard

So I've been reading Kierkegaard's Fear and Trembling. Kierkegaard argues that to find the greatest good, one needs to look no further than faith and he uses Abraham's test of faith to make his argument.

He argues that Abraham passed the test of faith not because he was willing to sacrifice Isaac, but because he fully intended to kill Isaac and at the same time, fully expected to keep Isaac (not a replacement heir, but Isaac himself).

He did not begrudgingly offer Isaac and thus lose his passion and he did not act like a madman to save Isaac's faith. Instead, he relied on the absurd idea that he could both sacrifice Isaac and still keep him.

My question to Kierkegaard is this: if we are to follow Abraham's example and have faith in the absurd, how can we tell which absurd we are to have faith in? There are many absurd ideas that we could put all our faith in that will not come to be. Granted, if there was something to tell us what absurd idea God wanted us to believe, then it would not take the same amount of faith.

What would happen if we spend our entire lives placing our faith in the absurd that never happens?

Is it because Abraham had faith that he would keep Isaac that he was allowed to keep him or did he just make a lucky guess when he decided to have faith in this absurd?

I haven't finished the book yet, so maybe these questions have yet to be answered.