According to WhatJewsBelieve.org the idea that God became flesh disagrees with the words of the Bible saying, "
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There is the verse from Hosea in which God specifically tells us that God is not a human being:
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I will not execute the fierceness of mine anger, I will not return to destroy Ephraim: for I am God, and not a man; the Holy One in the midst of thee: and I will not enter into the city. Hosea 11:9
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And then there is another verse, in Numbers 23:19, where God specifically tells us that if God were a human being, then he would be a liar, as all human beings do lie on occasion. Furthermore, this verse tell us that if God were a human being, he would be in need of repentance because all human beings sin at some point in their lives. Finally, this verse also tells us that if God were a human being, then he would make promises, but not keep them:
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God is not a man, that he should lie; neither the Son of Man, that he should repent: hath he said, and shall he not do it? or hath he spoken, and shall he not make it good? Numbers 23:19