And as these were being separated from him, Peter said to Jesus: ‘Instructor, it is fine for us to be here, so let us erect three tents, one for you and one for Moses and one for Elijah,’ he not realizing what he was saying.

The vision was so real that Peter began to participate in the scene, evidently overwhelmed with awe and appreciation. When he observed the two visionary men “being separated from [Jesus],” he apparently did not want them to leave. So he spoke about erecting tents, “not realizing what he was saying.”