Mt 16:16, Mt 24:14, Mt 28:18-19, Mk 16:15, Acts 1:8
The eternal gospel to be preached to all nations, tribes, tongues, and peoples is that Jesus is the Christ. (Rev 14:6, Mt 16:16)
Rev 14:6 And I saw another angel fly in the midst of heaven, having the everlasting gospel to preach unto them that dwell on the earth, and to every nation, and kindred, and tongue, and people,
Mt 16:16 And Simon Peter answered and said, Thou art the Christ, the Son of the living God.
We must spread the everlasting gospel that Jesus is the Christ throughout the world. (Mt 28:18-19, Mark 16:15, Acts 1:8)
Mt 28:18 And Jesus came and spake unto them, saying, All power is given unto me in heaven and in earth. 19 Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost:
Mark 16:15 And he said unto them, Go ye into all the world, and preach the gospel to every creature.
Acts 1:8 But ye shall receive power, after that the Holy Ghost is come upon you: and ye shall be witnesses unto me both in Jerusalem, and in all Judaea, and in Samaria, and unto the uttermost part of the earth.
The end of the world comes when Jesus is the Christ preached throughout the world. (Matthew 24:14)
Matthew 24:14 And this gospel of the kingdom shall be preached in all the world for a witness unto all nations; and then shall the end come.