The end-time message was promised by God in Malachi 4: 5 Behold, I will send you Elijah the prophet before the coming of the great and dreadful day of the LORD.
6 And he shall turn the heart of the fathers to the children, and the heart of the children to their fathers, lest I come and smite the earth with a curse.
and the first part of turning fathers' hearts toward their children was fulfilled in the time of John the Baptist and this was confirmed by Jesus himself Matthew 17:11 And he answered and told them, Elias verily cometh first, and restoreth all things;
12 But I say unto you, That Elias is come already, and they knew him not, but have done unto him whatsoever they listed. In the same way the Son of Man is going to suffer at their hands. Jesus says Elijah is coming because at that time he was still there. they started their own doctrines and denominations leaving the true teachings of the apostles and then they started teaching the doctrine of the trinity that God has three persons when in the bible there is one God with one soul and that is what they taught the prophets Isaiah: Chapter 44
6 Thus saith the LORD, the King of Israel, and thy Redeemer, the LORD of hosts; I am the first, and I am the last; besides me there is no God.
Isaiah: Chapter 48
11 For my own sake, for my own sake, will I do it; je! Should my name be defiled? And I will not give my glory to another.
God says he is one and the same person so the doctrine of the trinity does not come from God so in order for God to save the people who were lost in the heresy of evil people who changed the teachings of God to be worshiped they took the glory of God and gave themselves to them. a very holy father which is the attribute of God and this is the antichrist 2 Thessalonians: Chapter 2
4 the opposer, who exalts himself above all that is called God or that is worshiped; even sitting in the temple of God, shewing himself that he is God.
John: Chapter 17
11 And now I am no more in the world, but these are in the world, and I come to thee. Holy Father, keep through thine own name those whom thou hast given me, that they may be one, as we are.
so God gave Elijah the message of this generation to bring us back to the word of God and this Elijah is the prophet William Marrion Brahnam in a nutshell.