Can you give an example of one of these stories that you have a problem with?
That is a good example. As a parent myself I agree that it is nearly impossible for me to imagine sacrificing my son in the way that Abraham was instructed to do. The author of Hebrews in the New Testament has this to say about Abraham and Isaac:
By faith Abraham, when God tested him, offered Isaac as a sacrifice. He who had received the promises was about to sacrifice his one and only son, even though God had said to him, "It is through Isaac that your offspring will be reckoned." Abraham reasoned that God could raise the dead, and figuratively speaking, he did receive Isaac back from death. Hebrew 11:17-19 (NIV)
The idea being expressed here is that Abraham had such faith that he believed that God would fulfill his promise to him, even if God had to raise Isaac back from the dead to do it. In this case I think "faith" is better understood as being closer to "certainty" than what we mean by "faith" today. If you had the experiences with God that Abraham had by this time I would think you would be pretty certain that God could do what he promised.
I find it hard to imagine having the courage of Jesus in going forward knowing what awaited him at Gethsemane too.
But you are right. It is hard to imagine having the faith of Abraham, or Jesus such that one could do these things. But also again we run into the problem that "faith" to them is not what "faith" is to us. Both of them had overwhelming first hand evidence of the power of God.
I do agree with you that it is difficult to imagine doing either of these - nearly impossible for your average person. Whether it violates human psychology in all cases I don't know. I think it is pretty certain that almost all men and women could not have done what these men are supposed to have done. Abraham and Jesus were definitely exceptions to the rule.
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p.s. One other thought - if we really wanted to study the possible psychology here we would have to look at the psychology of a people at a stage of development similar to where Abraham was maybe 4,000 years ago. It was a very different psychology from how people in the first world think today.
For evidence consider this. In parts of the Muslim world which are pretty backward (which is most of it) it is still possible for a father to kill his daughter if she in some way embarasses the family (called "honor killings" or some such). Apparently this is not all that unusual.