Charles Ellicott Commentary John 15:21

"But all these things will they do unto you for my name`s sake, because they know not him that sent me." — John 15:21 (ASV)

But all these things will they do unto you.—These words are themselves an interpretation of the previous verse. They suppose the persecution and hatred to take place, and find the true consolation in the fact that this would be done to them as representing their Lord. The Acts of the Apostles and the Epistles are a commentary on this text. (Compare, among numerous passages, Acts 4:17; Acts 9:14; Galatians 6:17.)

Because they know not him that sent me.—The hatred is here traced to its true cause, which is ignorance of God. The Apostles were those sent by Christ. He Himself was the Apostle of the Father. They would hate His messenger, and hate Him, the messenger of God, because they did not know God.