{This is Elijah} (autos estin Eleias). Jesus here
endorses John as the promise of Malachi. The people understood
 Mal 4:1  to mean the return of Elijah in person. This John
denied as to himself ( Joh 1:21 ). But Jesus affirms that John is
the Elijah of promise who has come already ( Mt 17:12 ). He
emphasizes the point: "He that hath ears to hear, let him hear."