Luke 9:33

33 As the two men were about to leave Jesus, Peter said to him, "Master, it's good that we're here. We should construct three shrines: one for you, one for Moses, and one for Elijah"—but he didn't know what he was saying.

Luke 9:33 Meaning and Commentary

Luke 9:33

And it came to pass, as they departed from him
That is, as Moses and Elias departed from Christ; or "when they began to depart", as the Syriac version renders it; or "would depart", as the Arabic and Persic versions; seemed desirous of going, or made some signal or other by which the disciples perceived they were about to go; for, as yet, they were not gone;

Peter said unto Jesus, master, it is good for us to be here, let us
make three tabernacles, one for thee, and one for Moses, and one for
Elias; (See Gill on Matthew 17:4)

not knowing what he said,
nor "what to say", as Mark observes, being in a surprise, and not in a situation to consider and weigh things well, whether what he said was right and proper, or not; (See Gill on Matthew 17:4)

Luke 9:33 In-Context

31 They were clothed with heavenly splendor and spoke about Jesus' departure, which he would achieve in Jerusalem.

32 Peter and those with him were almost overcome by sleep, but they managed to stay awake and saw his glory as well as the two men with him.

33 As the two men were about to leave Jesus, Peter said to him, "Master, it's good that we're here. We should construct three shrines: one for you, one for Moses, and one for Elijah"—but he didn't know what he was saying.

34 Peter was still speaking when a cloud overshadowed them. As they entered the cloud, they were overcome with awe.

35 Then a voice from the cloud said, "This is my Son, my chosen one. Listen to him!"