Why would God choose David, such a sinner, adulterer and murderer to be King and why would He plan for Jesus to come from the house of David?

Nathan said to David: “Thus says the LORD God of Israel: ‘I anointed you king of Israel. I rescued you from the hand of Saul. I gave you your lord’s house and your lord’s wives for your own. I gave you the house of Israel and of Judah. And if this were not enough, I could count up for you still more. Why have you rejected the LORD and done evil in his sight? You have cut down Uriah the Hittite with the sword; you took his wife as your own, and him you killed with the sword of the Ammonites. Now, therefore, the sword shall never depart from your house, because you have looked down on me and have taken the wife of Uriah to be your wife.’” Then David said to Nathan, “I have sinned against the LORD.” Nathan answered David: “The LORD on his part has forgiven your sin: you shall not die.”

Brothers and sisters: We who know that a person is not justified by works of the law but through faith in Jesus Christ, even we have believed in Christ Jesus that we may be justified by faith in Christ and not by works of the law, because by works of the law no one will be justified. For through the law I died to the law, that I might live for God. I have been crucified with Christ; yet I live, no longer I, but Christ lives in me; insofar as I now live in the flesh, I live by faith in the Son of God who has loved me and given himself up for me. I do not nullify the grace of God; for if justification comes through the law, then Christ died for nothing.

A Pharisee invited Jesus to dine with him, and he entered the Pharisee's house and reclined at table. Now there was a sinful woman in the city who learned that he was at table in the house of the Pharisee. Bringing an alabaster flask of ointment, she stood behind him at his feet weeping and began to bathe his feet with her tears. Then she wiped them with her hair, kissed them, and anointed them with the ointment. When the Pharisee who had invited him saw this he said to himself, "If this man were a prophet, he would know who and what sort of woman this is who is touching him, that she is a sinner." Jesus said to him in reply, "Simon, I have something to say to you." "Tell me, teacher," he said. "Two people were in debt to a certain creditor; one owed five hundred days' wages and the other owed fifty. Since they were unable to repay the debt, he forgave it for both. Which of them will love him more?" Simon said in reply, "The one, I suppose, whose larger debt was forgiven." He said to him, "You have judged rightly." Then he turned to the woman and said to Simon, "Do you see this woman? When I entered your house, you did not give me water for my feet, but she has bathed them with her tears and wiped them with her hair. You did not give me a kiss, but she has not ceased kissing my feet since the time I entered. You did not anoint my head with oil, but she anointed my feet with ointment. So I tell you, her many sins have been forgiven because she has shown great love. But the one to whom little is forgiven, loves little." He said to her, "Your sins are forgiven." The others at table said to themselves, "Who is this who even forgives sins?" But he said to the woman, "Your faith has saved you; go in peace." Afterward he journeyed from one town and village to another, preaching and proclaiming the good news of the kingdom of God. Accompanying him were the Twelve and some women who had been cured of evil spirits and infirmities, Mary, called Magdalene, from whom seven demons had gone out, Joanna, the wife of Herod's steward Chuza, Susanna, and many others who provided for them out of their resources.