I'll wiegh in on this. I believe in the trinity and agree with Yorick's quotes for the sake of brevity I'll not repeat them.
An observation there is little if any disagreement on man being three in one (spiritual, physical, and mental) are we not created in the image of God? Gen.1:26 (side note "let US make man in Our Image" new american standard translation) Why is it hard to believe that the Creator, who (or whom) is greater than us is not capable of the same three in one?
Are His ways are ways? Are not His ways higher then our ways? Who amuongst (sp?) us can understand eternity? we have a grasp of the concept but do not understand.
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"the memories of a man in his old age,
are deeds of a man in his prime"