How was this prophecy fulfilled with Elijah's return?
Not an area that I personally have gone into great lengths to understand and I will not just follow what someone else says.
Neither have I gone onto the net to see what creations that man has no doubt done with it. 
So to eliminate the risk of me misleading by commenting on it, I really have nothing to say or add at this point in time.
After I had the trinity claws, angel of light cut out of me, 
went to war so to speak, my sights to quite a degree went to the old and repeated point, cries, --> just in the said Christian faiths, how come we have all these differing interpretations and if we have so many of them on track, truth, then the signs of this should be unquestionably clear in the world.
No way possible should we have the likes of pedophiles if they were on truth as it should be understood and feel like, that you actually doing that act before God and Jesus, no question about it.
Plus after Jesus and due to him, we have the One Spirit of truth (God) in the world, hence on what I refer to as the first milk as in who is who regarding God and Jesus = one and one only interpretation should be without question, which we do not have.
Hence we need to search the Bible for these answers.
God is Spirit the one Holy Spirit = most create another god the holy spirit here = that means you have to give God another spirit to replace it and you have created an idol out of the Holy Spirit.
He is Word, The Word = They give that to Jesus.
He is light the true light ref in John 1:9 = They give this to Jesus.
What's left of the Key basics of God = Zero and replaced with some strange spirit.
So naturally that then means, you have created another Jesus.
John 17:3 - This now is the eternal life, that they should know you, the only true God and whom you have sent, Jesus Christ.
Now the trinity say this "God" term here is in reference to god the father, god the son and god the holy spirit and because we have the and in here, this obviously becomes impossible, hence they will simply talk in circles trying to dodge this clear and obvious error.
Not to mention, there is zero reference here that you must believe in a god the holy spirit and the reason for that is because the Almighty God and Father IS This One Spirit.
So the above alone appears to answer the points or causes I make above?
IMO, if one was to sum up the Bible, God and Jesus the key theme or one word would be = WORD --> The Word --> The Word of God = God's way of communication to his creation.
Gen 1:1 Beginning created God Aleph Tav (et) -->(Word?) --> heavens and earth.
That has been the theme, battle from day one until now, keeping the word on track, truth.
The Bible says, God reveals the end from the Beginning.
So if we reverse that, man very early didn't follow The Word (a plan, intentional???) = it will be very late, near the end before man comes back on line to truth?
Many OT passages appear to keep repeating this theme.
רבד - DABAR= WORD
(Note – Hebrew letters have been changed to left to right to alignto the English way of reading)
DALETH = Door – Can be swinging or two-way.
BETH = House or Tent = SPIRIT/WORD
RESH=Head = Almighty God and Father.
So to come to God, His Word, is to come into him, effectively in his house, Comforter, House, Wall, Kingdom etc.
2 Sam 7:12-14 - Tells us, that when the times would be fulfill, he would send Jesus who literally only came into existence at Mary, to build a new House for God, Jesus being the cornerstone and Now the Door, the curtain was torn.
We are to build onto this corner Stone and the mortar is obviously The Word = The Word of God.
More of what you didn't ask for haha
