A.T. Robertson Commentary John 15:20

"Remember the word that I said unto you, A servant is not greater than his lord. If they persecuted me, they will also persecute you; if they kept my word, they will keep yours also." — John 15:20 (ASV)

Remember (μνημονευετε). Present active imperative of μνημονευω, old verb from μνημων, in John again in 16:4,21. See 13:16 for this word.

If they persecuted me (ε εμε εδιωξαν). Condition of first class. They certainly did persecute (first aorist active of διωκω, to chase like a wild beast like the Latin persequor, our "persecute") Jesus (5:16). They will persecute those like Jesus. Cf. 16:33; Mr 10:30; Luke 21:12; 1 Corinthians 4:12; 2 Corinthians 4:9; Galatians 4:29; 2 Timothy 3:12 for proof that this prophecy came true. But the alternative is true and is stated by Jesus with a like condition of the first class, "if they kept my word" (ε τον λογον μου ετηρησαν). The world does praise the word of Jesus, but dreads to follow it.