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. Then remembered they, etc. - After the ascension of Christ, the disciples saw the meaning of many prophecies which referred to Christ, and applied them to him, which they had not fully comprehended before. Indeed it is only in the light of the new covenant, that the old is to be fully understood.
Related Commentaries of John 12:16
John 12:16
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.