He uses alliteration in his speech to catch our attention,for example he says "we can not dedicate- we can not consecrate --we can not hollow this ground".Using alliteration is repeating the beggining phrase and in out mind we hear the reapeating sounds.This he uses it because they as an audience will be able to to distinguish certain sounds and that will stand out to us.
Lincoln also uses repetition in his speech to grab out attention ,for example he says"of the people,by the people ,for the people".Using repetition it repeats certain words or phrases and by doing that we are able to identify