Because for them without Jesus there is no Christianity, there is no *Christian* faith, there is no Christian-style 'salvation'. Jesus is all they have.\n\nImagine Buddhism without the Buddha.\n\nFor much of Christianity's history, it is/was a proselytising faith set up to spread much like the Borg of the delta quadrant fame.  You will be assimilated - resistance is futile.\n\nAnd for centuries, resistance was largely futile, until the renaissance period. \n\nYou should forgive most proselytisers. Most do not comprehend that their proselytising ways are often highly insulting and/or offensive to people of other religions and ways of life. They just can't see it.\n\nTo them, assimilating you into the collective is a good thing and they get the kudos of having 'saved you'.\n\nThe best way to respond is to ask them lots of questions about their faith's inconsistencies, most of which either hav no answers or have answers that involve an industrial-sized spinning machine. And always check out that their Bible quotes are correct as much gets mistranslated (from Greek/Hebrew into English) and/or taken out of its biblical context. And then you can find out if you're dealing with someone who's ignorant of the authentic biblical texts or someone who's wilfully trying to mislead you.\n\nA quick search on Yahoo for "response to christian missionaries" came up with this site:\nhttp://www.karaites-usa.org/Responding_To_Missionaries/\n\n\nHope  that helps.