i will preface this review by saying that what follows is my interpretation of what "fear and trembling" is about. kierkegaard probably would've wanted each individual reader to struggle with the meaning for him-or-herself, as that is what would make the reading of "fear and trembling" of any value to the reader.
there is a difference between the ethical and the religious. confusion over the two has caused great tragedy in human affairs in the past and will continue to do so in the future. kierkegaard's magnum opus "fear and trembling" deals with the relationship between the ethical and the religious spheres, and thus remains relevant even to a modern audience.
kierkegaard wrote "fear and trembling" because he felt the christianity of his time had become too easy, too sugar-coated for the masses to swallow. faith loses its importance when the church becomes more interested in expanding and maintaining its reach than in the underlying message; faith, by its very nature, should be a difficult thing to attain. like many reformers before him, kierkegaard saw christianity as corroding from within. on the other hand, hegelian philosophy had also spread across europe in the early nineteenth century and was encroaching on territories even outside of philosophy, given the ambitious scope of hegel's project. the philosophers were threatening to co-opt the spiritual through logic: hegel's self-realization of "geist," the german word for both "mind" and "spirit." it is in this setting that kierkegaard wrote his most important book, addressing the dangers to christianity from within and without.
"fear and trembling" should be read in the context of the rest of kierkegaard's pseudonymous works for its message to be understood. kierkegaard conceived of life as going through three stages: the aesthetic, the ethical and the religious. this framework is also tackled extensively, for example, in "either/or (volumes 1 and 2)" and "stages on life's way." the gist is that before one even attempts to have faith in god, one must first come to appreciate the world for its appeal to one's senses. after that, one matures and realizes there are more important things out there and one gives up his/her individual nature for the universal, living to serve the greater good. this ethical stage can be reached by anybody and is different from being religious. in particular, people of all religions or lack thereof can be ethical people and sacrifice their own selfish needs for others. the ethical stage is where all organized religions and even atheism overlap, and this common ground is all that's needed for a peaceful civilized society.
now, to go from the ethical to the religious stage requires one to abandon the universal, reasserting the individual over the common good, but not regressing to the aesthetic stage in the process either. rather, one undergoes a trial of faith and mysteriously leaps to faith. i say "mysteriously" because faith is a very personal thing between god and the individual. that leap to faith cannot be explained by appealing to logic, nor can what occurs during the trial of faith be effectively communicated or understood by others. on top of all that, the trial of faith will bring the ethical individual into conflict with the ethical itself, hence the "trial" part. it is inconceivably hard and seemingly impossible to attain faith precisely because one must have genuinely gone through the ethical stage first and yet be forced to abandon the ethical.
kierkegaard illustrates all of these ideas in the story of god's command for abraham to sacrifice isaac at mount moriah. faith is something that could take a lifetime to achieve given the earlier stages one must go through; abraham was an old man when he faced his trial so even the patriarch of the judeo-christian tradition is not exempt from the long hard journey through the stages on life's way. god's command to sacrifice isaac very clearly and unequivocally conflicts with the ethical. abraham intended to go through with the sacrifice, but is stopped by god after abraham passes the trial. what exactly occurred in abraham's mind, let alone god's mind, during the trial cannot be known to anyone else. we only see a good person about to do a very bad thing, ready to give everything up and yet receiving it all back by god's will. faith must be absurd, hence ultimately impervious to philosophical/logical investigation. and with this one carefully chosen example, kierkegaard masterfully defended christianity from the dangers on both fronts mentioned earlier.
sometimes kierkegaard's breaking of his engagement to regine olsen is mentioned as a potential source of meaning for "fear and trembling." in particular, some folks posit that kierkegaard was hoping to receive regine olsen back after the breaking of the engagement, much as the knight of faith in "fear and trembling" receives the world back, by virtue of the absurd. it is certainly true that kierkegaard was deeply affected by this episode in his life, but one of the reasons he broke off the engagement was because he wanted to focus on the deeper theological and religious issues he felt he should devote his life to. i have too much respect for kierkegaard's grand project to give this very personal interpretation much weight.
there are two main english translations of "fear and trembling" available: the one done by walter lowrie, and the one done by edna and howard hong. the hongs' translation for the princeton "kierkegaard's writings" series is the superior translation, in my opinion. lowrie's older translation is outdated and some of his choice of words will distract you. for example, the lowrie translation includes the phrase "a panegyric upon abraham" while the hongs translated the same as "eulogy on abraham." take your pick!
the princeton "kierkegaard's writings" series is excellent in general, offering excerpts from kierkegaard's journals as well as historical/philosophical context for kierkegaard's work. "fear and trembling" is packaged with "repetition" in volume 6 of the series, but you should really think of the vastly overshadowed "repetition" as just a nice bonus.
on a personal note, i read and kept re-reading "fear and trembling" on the side in the spring semester of my sophomore year in college. i majored in electrical engineering, but much of my focus was on this book instead. compared to the subject matter kierkegaard was dealing with, everything else just seemed so incredibly trivial. even after the four years of classes to complete my degree, i find that "fear and trembling" is still what i think about more. i hope kierkegaard has as much of an influence on your life as he has had on mine.