Watch the video in my last post, to get an idea of the mythology behind what is being said by Socrates here. After listening to a speech laying out the origin of love, Socrates gives a speech in response, basically shooting down everybodies ideas like he always does, and in the midst of that speech he says this:
"And you hear people say that lovers are seeking for their other half; but I say that they are seeking neither for the half of themselves, nor for the whole, unless the half or the whole be also a good. And they will cut off their own hands and feet and cast them away, if they are evil; for they love not what is their own, unless perchance there be some one who calls what belongs to him the good, and what belongs to another the evil. For there is nothing which men love but the good. Is there anything?"
This touches on so many Socratic ideas it is hard to get started. He so offhandedly remarks that a man is willing to chop off body parts here that it can be difficult to take him seriously. I know that often when there was a physical deformity in those times the only thing to do was to amputate, and in that sense if your foot was no good you would of course cut it off. To Plato and Socrates, to be good meant to be pleasant or useful. If your hand was neither, it would be better not to have to deal with it. I have a friend who had problems with his foot for a number of years. It wasn't crippling, but it hurt him all the time. Eventually he cut it off and got a prosthesis to get rid of the problem. This may be similar to what Socrates had in mind here.
In another sense though, Plato (not Socrates) may be calling attention to Socrates death in this piece. Socrates was a man who, according to what we know, died rather than give up his conception of good. Here he is simply stating his modus operundi, to seek the good regardless. Hands and feet are simply a part of our mortal and changing bodies, but the good is eternal, and to partake in the good is to enter in to the eternal. In that quest, the casualty of some ancillary parts is unimportant.
A few hundred years later we get to Jesus, who says something similar in Matthew 5:
If your right eye causes you to stumble, gouge it out and throw it away. It is better for you to lose one part of your body than to be thrown whole into Gehenna. And if your right hand causes you to stumble, cut it off and throw it away. It is better for you to lose one part of your body than to be thrown whole into Gehenna.
In this passage, there isn't any chance of taking him to mean "if your eye or hand is no longer useful", he is clearly speaking of moral stumbling (the specific context is adultery). Jesus here is setting up a moral standard, and setting that standard against our desire to preserve ourselves. Just as losing an eye or a hand is serious business, so too is losing a sense of our moral standard.
Though many people I know profess to follow the bible literally, I know of not one person who has taken Jesus at his word here. I think that if somebody did try to gouge out his eye because he looked at a woman in lust, most would think that person a bit crazy. Most of us tend to try to look at this verse in a less severe way, because nobody really wants to maim themselves for any reason, despite what Socrates said so offhandedly a few hundred years earlier.
There are 2 things we do to make this verse make sense in our modern world. One is to spiritualize it in the "Jesus just means we need to get rid of anything in our lives that keep us from loving God." The other is to say that he meant what he said, but that our eyes and hands don't cause us to sin, it is our hearts. I think he was more serious though.
There is a large theme in the NT of "death to self" that dovetails nicely with what Jesus is saying here. Paul talks about the spirit being willing but the flesh being weak. There is much talk about being "dead to sin but alive in Christ." The idea here is that there are two warring factions within you; the soul, and the body in which the soul resides. We might call them our animal nature and our higher nature, or mind/body dualism. The goal is to live in accordance with our higher nature, which is the part "made in the image of God".
Jesus (and Paul) are telling us to do things to subjugate our body for the sake of our soul. He wants us to do things to let our body know who is in charge, even if it means hurting the vessel in which we reside. I don't know whether or not he actually wants us to cut off limbs (I tend to think he was using hyperbole here) but there is a definite call to live with our bodies as prisoners to our soul, instead of the other way around.
Finally we come to the modern period, and a good visual illustration of this very subject.
Warning: This video is rather gross (though fake) and not safe for work.
Here We can see the absurdity of a part of the body not acting in accordance with our will. Clearly in this situation there was nothing Bruce Campbell could have done other than cut off his hand with a chainsaw. The thing that makes this scene so funny and disturbing is that we can't imagine things going so wrong that our body rebels against us. There is no moral to the story because the whole situation is just bad. He is obviously not responsible for the actions of his hand at this point, but in all actuality, can we even call it "his" hand anymore? Once it gains the ability to rebel, it obviously has some sort of sentience and is responsible for whatever mischief it causes.
I have lots more I could say on all these things, but I tend to ramble, so I am going to cut this off. Let me know if there is anything in here you want to hear more about.