Help with Theme

[keif]

I feel that I understand theme on an intellectual level, but I'm trying to acquire an ingrained knowingness of how to use it in story. When people explain it in famous stories I can see it clearly, but I have a hard time applying it to my own stories.

I'm hoping someone can give me advice on how to extract theme from the following premise:

A man kills a stranger in order to save his dying wife.

I know this is bare bones and general. There are things that come to mind such as: "Murder is justified in circumstance." Or, "Life is dog eat dog."

I know there can be many explanations, I'm just trying to find one that gives me that "ah-ha" feeling. Thanks!

[Panglossian]

A man kills a stranger in order to save his dying wife.

I'm guessing, but it sounds like there might be a paranormal aspect to this story, in that the man somehow discovers that if he murders a random stranger he can reverse his wife's condition and prolong her life... If so, the theme would be love, desperate love, extreme love - a crime for love; a life for love; a death for the dying. So the theme would be love & death; Eros & Thanatos. - I'm just thinking aloud and may be well off the mark.