Luke 9:33

33 When Moses and Elijah were about to leave, Peter said to Jesus, "Master, it is good that we are here. Let us make three tents -- one for you, one for Moses, and one for Elijah." (Peter did not know what he was talking about.)

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 appeared in heavenly glory, talking about his departure which he would soon bring about in Jerusalem.

32 Peter and the others were very sleepy, but when they awoke fully, they saw the glory of Jesus and the two men standing with him.

33 When Moses and Elijah were about to leave, Peter said to Jesus, "Master, it is good that we are here. Let us make three tents -- one for you, one for Moses, and one for Elijah." (Peter did not know what he was talking about.)

34 While he was saying these things, a cloud came and covered them, and they became afraid as the cloud covered them.

35 A voice came from the cloud, saying, "This is my Son, whom I have chosen. Listen to him!"