Re. 14:6 Then I saw another angel flying in mid-air, and he had the eternal gospel to proclaim to those who live on the earth — to every nation, tribe, language and people.
Re. 14:7 He said in a loud voice, “Fear God and give him glory, because the hour of his judgment has come. Worship him who made the heavens, the earth, the sea and the springs of water.”

Job 1:8 Then the LORD said to Satan, “Have you considered my servant Job? There is no-one on earth like him; he is blameless and upright, a man who fears God and shuns evil.”
Job 1:9 “Does Job fear God for nothing?” Satan replied.

Ec. 12:13 Now all has been heard; here is the conclusion of the matter: Fear God and keep his commandments, for this is the whole duty of man.
Ec. 12:14 For God will bring every deed into judgment, including every hidden thing, whether it is good or evil.

"Fear God" is all about obeying God's commandments and keeping His Law. It is not about "faith and not works". It is not about receiving Jesus into your heart, but about doing the will of God.

Mt. 24:14 And this gospel of the kingdom will be preached in the whole world as a testimony to all nations, and then the end will come.

The gospel of the kingdom that Jesus talks about in Mt. 24:14 is obviously the eternal gospel of Re. 14:6. Today's gospel is just a temporary thing, which Jesus will make sure is thrown away before the end of the age.