Luke 9:33

33 And it happened that as they were going away from him, Peter said to Jesus, "Master, it is good [for] us to be here. And let us make three shelters, one for you and one for Moses and one for Elijah," not knowing 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 who appeared in glory [and] were speaking [about] his departure which he was about to fulfill in Jerusalem.

32 Now Peter and those with him were {very sleepy}, but [when they] became fully awake, they saw his glory and the two men who were standing with him.

33 And it happened that as they were going away from him, Peter said to Jesus, "Master, it is good [for] us to be here. And let us make three shelters, one for you and one for Moses and one for Elijah," not knowing what he was saying.

34 And [while] he was saying these [things], a cloud came and overshadowed them, and they were afraid as they entered into the cloud.

35 And a voice came from the cloud, saying, "This is my Son, [my] Chosen One. Listen to him!"