Imperfect tense: better, was declaring, all along through the prophetic age, in successive prophets. See the same verb in 1Co 3:13; 2Pe 1:14 :.
When it testified beforehand (προμαρτυρόμενον)
Only here in New Testament.
Of Christ (εἰς Χριστὸν)
Lit., unto Christ. So Rev., in margin. The sufferings destined for Christ, as in 1Pe 1:10 he speaks of the grace, εἰς ὑμᾶς, unto you; i.e., destined to come unto you. Peter was especially concerned to show that the sufferings of Christ were in fulfilment of prophecy, because it was a subject of dispute with the Jews whether the Christ was to suffer (Act 3:18; Act 26:22, Act 26:23).
The glory (τὰς δόξας)
Rev., correctly, the glories. The plural is used to indicate the successive steps of his glorification; the glory of his resurrection and ascension, of the last judgment, and of the kingdom of heaven.