This (so most translations; New American Bible “all this”) is literally “these things,” and is in the emphatic position in the Greek sentence structure. The plural form is used here in a collective sense and so may legitimately be rendered by the singular this.
The verb translated understand normally means “to know,” but the meaning “to understand” is obvious in the present context and so appears in most translations.
At the time (so also New English Bible, Goodspeed, Phillips, Jerusalem Bible) is literally “at first” (as in many translations). The phrase is used here to contrast the disciples’ understanding when these events were taking place with their understanding when Jesus was raised to glory. For this purpose the translation “at the time” is better than “at first.” In some languages it may be necessary to make more specific the reference to this and to stipulate more clearly the reference to time. Therefore one may translate “At the time these events took place his disciples did not understand what they meant” or “… did not understand all that was involved” or “… just what all of these happenings were pointing to.”
When Jesus had been raised to glory (Die Bibel im heutigen Deutsch “but when Jesus was raised in the glory of God”) is literally “when Jesus was glorified.” The reference is obviously to Jesus’ resurrection or exaltation, and the rendering in Good News Translation and Die Bibel im heutigen Deutsch make this information explicit. This same expression is used in John 7.39. Also see 2.22, where the phrase was raised from death is used with a meaning equivalent to raised to glory in this verse. To indicate clearly that raised to glory refers not only to the resurrection but also to the glorious results of that event, it may be necessary to translate in some languages “when Jesus had been brought back to life and made wonderful” or “… been brought back to life in a wonderful way.”
That the scriptures said this about him is literally “that these things were written about him.” But here, as elsewhere in the New Testament, “was written” is a reference to the Jewish scriptures (see verse 14 and 2.17). Said this about him may be rendered “said that this would happen to him” or “said that this is what he would experience.”
They had done this for him may be interpreted in several ways, depending on whom the subject they is assumed to be. Good News Translation (so also Phillips, Die Bibel im heutigen Deutsch, Bible en français courant, La Sainte Bible: Nouvelle version Segond révisée) takes they as a reference to his disciples at the beginning of the verse, since they are apparently the subject throughout the verse. Grammatically this is the simplest solution, though it is difficult to know what action is referred to in had done this for him, unless it is their procuring the donkey, which is not mentioned in John’s account. It is possible also to understand the crowd to be the subject of this verse, and so to translate with New American Bible “they recalled that the people had done to him precisely what had been written about him.” This may also be the meaning of Jerusalem Bible (“but later … they remembered that this had been written about him and that this was in fact how they had received him”) but this translation is not clear. Finally, it is possible to take they as an impersonal construction equivalent to a passive (Moffatt “then they remembered how this had been written of him and had happened to him”). This passive construction is followed also by New English Bible, Zürcher Bibel, and Luther. The simplest solution grammatically is to assume with Good News Translation that they refers to his disciples, even though it is not clear precisely what the disciples had done for Jesus. It is, of course, possible to understand his disciples in the sense of the larger group of followers, who would remember that on this occasion they had participated in praising Jesus as he entered into Jerusalem.
Quoted with permission from Newman, Barclay M. and Nida, Eugene A. A Handbook on the Gospel of John. (UBS Handbook Series). New York: UBS, 1980. For this and other handbooks for translators see here .