Excellent point, Emily.  We start with the passion of Christ, His suffering and death on the Cross, and then extend that idea to the suffering of the martyrs.  We can then further extend that sense of strong emotional desire, to paraphrase from above, to the realm of romantic, and/or sexual love.  We can extrapolate, that a person may well be willing to make great sacrifices for the one he or she is romanticly or sexually attached to (perhaps even going so far as to die for that other person, if  sufficienty passionate).  Love of family, or country stirs this same degree of passion, as can the dedication to certain ideas - "liberty", "freedom" etc.  Of course, one can make the argument that certain ideas of political philosophy have taken the place of religion for many, which brings us back, symbolicly, to Christ's passion on the Cross in sense one of the word.  Politcal philosophy as modern religion is, perhaps, a topic for another thread.  From this point on, however, we have a sense of diminished returns for our passion. As with many words that originated with a religious connotation, passion has suffered in status the further it is removed from the original context, which brings us to our current use of the word to describe anything one likes or approves of.  While many music fans might claim to feel passionate about a particular pop band or singer, it is doubtful they would lay thier lives down for thier favorite singer.