Isa 52:7, Isa 61:1, Lk 24:44-47, Mt 28:18-20, Acts 1:8
In the Old Testament, Isaiah told the evangelists to preach the good news: the salvation and reign of God. (Isa 40:9, Isa 52:7)
Isa 40:9 O Zion, that bringest good tidings, get thee up into the high mountain; O Jerusalem, that bringest good tidings, lift up thy voice with strength; lift it up, be not afraid; say unto the cities of Judah, Behold your God!
Isa 52:7 How beautiful upon the mountains are the feet of him that bringeth good tidings, that publisheth peace; that bringeth good tidings of good, that publisheth salvation; that saith unto Zion, Thy God reigneth!
In the Old Testament, Isaiah prophesied that the Spirit of God would come upon Christ and that Christ would heal and preach the gospel. (Isa 61:1)
Isa 61:1 The Spirit of the Lord God is upon me; because the Lord hath anointed me to preach good tidings unto the meek; he hath sent me to bind up the brokenhearted, to proclaim liberty to the captives, and the opening of the prison to them that are bound;
The Old Testament contains the record of the coming Christ. Jesus revealed to his disciples that he was the Christ recorded in the Old Testament. (Luke 24:44-47)
Luke 24:44 And he said unto them, These are the words which I spake unto you, while I was yet with you, that all things must be fulfilled, which were written in the law of Moses, and in the prophets, and in the psalms, concerning me. 45 Then opened he their understanding, that they might understand the scriptures, 46 And said unto them, Thus it is written, and thus it behooved Christ to suffer, and to rise from the dead the third day: 47 And that repentance and remission of sins should be preached in his name among all nations, beginning at Jerusalem.
The resurrected Jesus told us to preach the gospel, that is, that Jesus is the Christ, to the whole world. Through us, this gospel will be preached to the whole world. (Matthew 28:18-20, Acts 1:8)
Matthew 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: 20 Teaching them to observe all things whatsoever I have commanded you: and, lo, I am with you always, even unto the end of the world. Amen.
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.