Luke 9:33

33 And it was done, when they departed from him, Peter said to Jesus, Commander, it is good that we be here, and make we here three tabernacles, one to thee, and one to Moses, and one to Elias. And he knew not what he should say. [And it was done, when they departed from him, Peter saith to Jesus, Commander, it is good to us for to be here, and make we here three tabernacles, one to thee, and one to Moses, and one to Elias; not witting what he should say.]

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 were seen in majesty; and they said his going out, which he should fulfill in Jerusalem.

32 And Peter, and they that were with him, were heavy of sleep [were grieved, or heavied, with sleep], and they waking saw his majesty, and the two men that stood with him.

33 And it was done, when they departed from him, Peter said to Jesus, Commander, it is good that we be here, and make we here three tabernacles, one to thee, and one to Moses, and one to Elias. And he knew not what he should say. [And it was done, when they departed from him, Peter saith to Jesus, Commander, it is good to us for to be here, and make we here three tabernacles, one to thee, and one to Moses, and one to Elias; not witting what he should say.]

34 But while he spake these things, a cloud was made, and overshadowed them; and they dreaded, when they entered into the cloud.

35 And a voice was made out of the cloud, and said [saying], This is my dear-worthy Son, hear ye him.