Here are two videos that are only audio tracks of John MacArthur. The first one shows WHY God sends the Tribulation and who it's for. It's only 5 minutes.
The second video (wouldn't let me embed, so it's just a link) outlines who MacArthur believes the 24 elders are that John sees, and reasons why. Fascinating. Only 3:33 minutes. Give them a watch. I have to say the teaching on the elders is the most convincing I've heard for why MacArthur believes as he does.