Isa 52:7, Isa 40:9, Isa 61:1, Nahum 1:15, Rom 10:15-17, Acts 5:42
The Old Testament prophesied that the gospel of the kingdom of God would be preached. (Isa 52:7, Isa 40:9, Isa 61:1, Nahum 1:15)
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!
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 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;
Nahum 1:15 Behold upon the mountains the feet of him that bringeth good tidings, that publisheth peace! O Judah, keep thy solemn feasts, perform thy vows: for the wicked shall no more pass through thee; he is utterly cut off.
The law and the words of the prophets were preached only until the time of John the Baptist. After that, the gospel of the kingdom of God is preached. (Lk 16:16)
Lk 16:16 The law and the prophets were until John: since that time the kingdom of God is preached, and every man presseth into it.
Now the gospel of the kingdom of God is preached. That is, the gospel that Jesus is the Christ is preached. (Rom 10:15-17, Acts 5:42)
Rom 10:15 And how shall they preach, except they be sent? as it is written, How beautiful are the feet of them that preach the gospel of peace, and bring glad tidings of good things! 16 But they have not all obeyed the gospel. For Esaias saith, Lord, who hath believed our report? 17 So then faith cometh by hearing, and hearing by the word of God.
Acts 5:42 And daily in the temple, and in every house, they ceased not to teach and preach Jesus Christ.