There is nothing controversial in the claim that the king of Israel was thought of as standing in a uniquely close relationship to God and was in that sense considered the Son of God.
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Moreover, this son of David will be chosen by God himself, adopted as it were, to be his own son: "I will raise up your offspring after you, who shall come forth from your body, and I will establish his kingdom. He shall build a house for my name; and I will establish the throne of his kingdom forever. I will be a father to him,and he shall be a son to me."