The best way to do this right now is to "mute" channels by clicking the bell icon on the right of the channel header (or opening the server notification settings, or right-clicking the channel name). You can then easily hide all muted channels, providing a good way to get a condensed or filtered view of large servers.

At the end of the day Discord is a chat for gamers and gaming so features like that and searchable history aren't implemented yet because they're not things gamers usually use. They'll come eventually though.