"To discard the rest" means to get rid of or throw away everything else except for a specific thing or a few things that are important or useful. Full definition
They select the most frequent answer and discard the rest of the data as noise. (scientificamerican.com)
No one knows who wrote the bible, but it was compiled by men who included what books supported their views, then discarded the rest. (religion.blogs.cnn.com)
Sure, there are some good passages in there, but you can't just discard the rest of it, as much as today's watered - down, cherry - picking Christians would like to try. (religion.blogs.cnn.com)