Exegesis:
kai egeneto ‘and it happened,’ cf. on 1.8.
en tō diachōrizesthai autous ap’ autou lit. ‘at/during their parting from him,’ i.e. ‘as they were (already) parting from him.’
diachōrizomai ‘to part from’ (with apo), without indicating, or, implying how the departure took place.
epistata ‘master,’ cf. on 5.5.
kalon estin hēmas hōde einai ‘it is a good thing that we are here,’ a statement rather than an exclamation, hēmas refers to the three disciples.
kai poiēsōmen ‘and let us make,’ hortatory subjunctive, explaining for what purpose it is good that they are there.
skēnas treis ‘three booths.’ skēnē also 16.9.
mē eidōs ho legei ‘not knowing what he was saying,’ because he did not understand the situation.
Translation:
The first clause may have to be co-ordinated, e.g. ‘Next (or, another particle indication transition without specifying the length of time elapsed) the men were parting. At that moment Peter….’
The men, i.e. Moses and Elijah; hence “these” (The Four Gospels – a New Translation), ‘the two men’ (some Indonesian languages).
Were parting from him, or, “were leaving Jesus” (Good News Translation), “were moving away from Jesus” (New English Bible), ‘would withdraw from his presence’ (Javanese, using a reverent form here, because Jesus is the person they were parting from).
Master, see on 5.5.
It is well that we are here, or, “it is a good thing that we are here” (The Four Gospels – a New Translation), ‘it is fortunate that we are at hand.’ The pronoun has been taken as an inclusive, but the exclusive is probably preferable (see Exegesis).
Let us make three booths. The pronoun is exclusive; in Ekari the use of the exclusive form implies that the building is done for the benefit of others (i.e. Jesus, Moses, and Elijah) exclusive of the performer(s) (i.e. the disciples). The verb is often better rendered by ‘to build,’ or by any other specific verb commonly used for the setting up of booths (or, ‘huts,’ ‘shelters’).
Not knowing what he said, or resuming here the verb with which this phrase goes, ‘but he spoke (or, said so) without knowing what he was saying’ (cf. New English Bible). Of course Peter knew what he said, in the sense that he understood his own words, but he didn’t realize that his proposal was out of place; hence more specific renderings such as, ‘not conscious of…’ (Bahasa Indonesia), .’.. the purport of these words of his’ (Balinese), ‘as-a-matter-of-fact this word-of-his was without thinking’ (Javanese).
Quoted with permission from Reiling, J. and Swellengrebel, J.L. A Handbook on the Gospel of Luke. (UBS Handbook Series). New York: UBS, 1971. For this and other handbooks for translators see here . Make sure to also consult the Handbook on the Gospel of Mark for parallel or similar verses.