I play mc on a Mac and I tried downloading a resource pack. When I tried to relaunch Minecraft the loading screen would pop up but the page with single player, multiplayer, [etc.] wouldn't open and either the launcher would pop back up and there would be a crash report or the loading screen would just close. When I would get the crash reports it said that the resource pack I downloaded was too big(1024x1024) and I should try a lower resolution but I wasn't able to access options(on the page that usually came up after loading screen) and change to the original resource pack. I'm trying to find ways around this and I did try reinstalling Minecraft and logging back in which didn't work.
Use optifine.