GOD's unalterable promise to David:
Psa 89:34 My covenant will I not break, nor alter the thing that is gone out of my lips.
Psa 89:35 Once have I sworn by my holiness that I will not lie unto David.
Psa 89:36 His seed shall endure for ever, and his throne as the sun before me.
Psa 89:37 It shall be established for ever as the moon, and as a faithful witness in heaven. Selah.
Confirming the unalterable promise to Mary by the angel Gabriel:
Luk 1:31 And, behold, thou shalt conceive in thy womb, and bring forth a son, and shalt call his name JESUS.
Luk 1:32 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:
Luk 1:33 And he shall reign over the house of Jacob for ever; and of his kingdom there shall be no end.
Scripture defining the throne of David:
2Sa 3:10 To translate the kingdom from the house of Saul, and to set up the throne of David over Israel and over Judah, from Dan even to Beersheba.
Rom 3:28 Therefore we conclude that a man is justified by faith without the deeds of the law.
Rom 3:29 Is he the God of the Jews only? is he not also of the Gentiles? Yes, of the Gentiles also:
Rom 3:30 Seeing it is one God, which shall justify the circumcision by faith, and uncircumcision through faith.
Act 2:29 Men and brethren, let me freely speak unto you of the patriarch David, that he is both dead and buried, and his sepulchre is with us unto this day.
Act 2:30 Therefore being a prophet, and knowing that God had sworn with an oath to him, that of the fruit of his loins, according to the flesh, he would raise up Christ to sit on his throne;
Act 2:31 He seeing this before spake of the resurrection of Christ, that his soul was not left in hell, neither his flesh did see corruption.
Act 2:32 This Jesus hath God raised up, whereof we all are witnesses.
Act 2:33 Therefore being by the right hand of God exalted, and having received of the Father the promise of the Holy Ghost, he hath shed forth this, which ye now see and hear.
Act 2:34 For David is not ascended into the heavens: but he saith himself, The LORD said unto my Lord, Sit thou on my right hand,
Act 2:35 Until I make thy foes thy footstool.
Act 2:36 Therefore let all the house of Israel know assuredly, that God hath made that same Jesus, whom ye have crucified, both Lord and Christ.