John Gill Commentary John 12:16

"These things understood not his disciples at the first: but when Jesus was glorified, then remembered they that these things were written of him, and that they had done these things unto him." — John 12:16 (ASV)

These things understood not his disciples at the first ,
&c.] Or "at that time", as the Syriac and Persic versions render it; or "on that day", as the Ethiopic version; they did not then know the sense of that prophecy, nor that the things which were now doing were a fulfilling of it:

but when Jesus was glorified ;
was raised front the dead, and ascended to heaven, and was set down at the right hand of God, crowned with glory and honour; and when having received the promise of the Father, the Holy Ghost, and his gifts, he poured them forth in a very plenteous and extraordinary manner upon them; whereby their minds were greatly illuminated, and they had a very distinct knowledge of the Scriptures of the Old Testament; and saw clearly how they severally had their accomplishment in Christ:

then remembered they that these things were written of him ;
in the prophecies of the Old Testament;

and [that] they had done these things unto him ;
both the disciples and the multitude, or that these things were done to him; such as bringing the ass to him, laying their clothes on it, and setting him upon it, attending him with shoutings and hosannas to the city of Jerusalem