Albert Barnes on Matthew 17:4

Let us make here three tabernacles. A tabernacle is a tent. It was made commonly by fixing posts into the ground, and stretching on them cloth, fastened by cords. Isa 33:20. In some instances, they were made of branches of trees;--a temporary shelter from the sun and rain, not a permanent dwelling. Peter was rejoiced at the vision, and desirous of continuing it. He proposed, therefore, that they should prolong this interview, and dwell there. Mark adds, that they knew not what they said in proposing this. They were frightened, amazed, and rejoiced; and, in the ecstasy of the moment, they proposed to remain there.