2 Sam 7:12-13, 16, Ps 132:11, Isa 9:6-7, Isa 16:5, Jer 23:5
In the Old Testament it was foretold that Christ would receive the throne of David forever. (2 Sam 7:12-13, 16, Ps 132:11, Isa 9:6-7, Isa 16:5, Jer 23:5)
2 Sam 7:12 And when thy days be fulfilled, and thou shalt sleep with thy fathers, I will set up thy seed after thee, which shall proceed out of thy bowels, and I will establish his kingdom. 13 He shall build an house for my name, and I will stablish the throne of his kingdom for ever. 16 And thine house and thy kingdom shall be established for ever before thee: thy throne shall be established for ever.
Ps 132:11 The Lord hath sworn in truth unto David; he will not turn from it; Of the fruit of thy body will I set upon thy throne.
Isa 9:6 For unto us a child is born, unto us a son is given: and the government shall be upon his shoulder: and his name shall be called Wonderful, Counsellor, The mighty God, The everlasting Father, The Prince of Peace. 7 Of the increase of his government and peace there shall be no end, upon the throne of David, and upon his kingdom, to order it, and to establish it with judgment and with justice from henceforth even for ever. The zeal of the Lord of hosts will perform this.
Isa 16:5 And in mercy shall the throne be established: and he shall sit upon it in truth in the tabernacle of David, judging, and seeking judgment, and hasting righteousness.
Jer 23:5 Behold, the days come, saith the Lord, that I will raise unto David a righteous Branch, and a King shall reign and prosper, and shall execute judgment and justice in the earth.
An angel appeared to Mary and told her that Jesus, who would be born in her body, would receive the throne of David forever. In other words, Jesus who will be born in the body of Mary is the Christ. (Lk 1:30-33)
Lk 1:30 And the angel said unto her, Fear not, Mary: for thou hast found favour with God. 31 And, behold, thou shalt conceive in thy womb, and bring forth a son, and shalt call his name Jesus. 32 He shall be great, and shall be called the Son of the Highest: and the Lord God shall give unto him the throne of his father David: 33 And he shall reign over the house of Jacob for ever; and of his kingdom there shall be no end.