The Third Elijah, The 144 000 & A Double Portion

In Episode 121 we discuss the Third Elijah, referring to the remnant church and the message that they have to proclaim to the world, which is the same message as the first Elijah. This same message is the message that will be proclaimed by the 144 000 of Revelation. But the third Elijah will need a double portion of the Spirit of the First Elijah. What is this message that has to be carried to the ends of the earth?