Jesus is here ranslating into Greek, and interpreting it to the disciples with figurative-literal language, where Elias (Elijah pronounces as in Greek or in Ger=man) is symbolic of John Baptizer's ministry to which he has been summoned and ordained, for people to turn to God from sin and thus gain a mindset that can accept Jesus as being plain-literally God-come-in-human-flesh Messiah.
You might note that much of Jesus; training in His three-and-a-half year stint with them was accustoming them to the use of plain-literal and figurative-literal language in arriving at a literal interpretation of the Scriptures (not a Romanistic allegorical one).
This hasn't worked too well where CatholicISM is concerned.