For this reason it is specifically important to hear the megillah reading in as large a gathering of Jews as one can find. [Which is cool, because we might think that since there is such a mitzwah to hear each word of the megillah, it is important to break into small groups with the least number of distractions--in actuality, we should be banding together into larger and larger groups.]
This is also why Amalek attacked the stragglers, the Jews who were forced out of the unity by the divine clouds (that surrounded the nation) because of their questionable backgrounds. It is for this reason that when we put on our talit gadol and gather in the tztziyot during birchot shema, we should have the intention (כוונה) to gather in all those souls who have been pushed to the outside. Since the Tzitzith represent the divine clouds with which HaShem surrounds Bnei Yisrael. Through tzitzith we join and unify the whole of Am Yisrael. [see an earlier post on the subject here]
Through tzitzith we keep amalek at bay.