Jesus took a couple of disciples up the mountain to have a holy experience that they could observe. His clothes and face shown maybe like it did when He had lived in heaven. Moses and Elijah were there also. They were talking for a while.
Then Peter began to speak and said to Jesus, Lord, it is good and delightful that we are here; if You approve, I will put up three booths here–one for You and one for Moses and one for Elijah. (Matthew 17:4 AMP)
Peter, being hospitable, a little ADD, and very cute said "Lord it's delightful they're here. Let's set up booths (or little shelters) so they can stay the night!" Peter missed the holiness and sacredness of the moment. Poor thing, God immediately spoke in His holiest, very powerful and frightening voice that He was pleased with His Son. All the disciples fell flat on their faces and the moment was over. Jesus touched them and told them it was OK. Elijah and Moses were gone.
Peter catches it for not getting that this was a holy, sacred moment. I've done that sometimes. A friend will tell me a pain in her life and I'll talk a little then ask what she wants for lunch. I'm ADD and insensitive at times. Peter at least was being hospitable. It was kind of a Martha moment. He was missing out on the sacred to hustle and bustle like Martha.