Transfiguration and Transformation

Our Bibles consistently use the noun ‘Transfiguration’ with regard to Jesus but ‘Transformation’ with regard to the Christian – and yet it is one and the same verb, transliterated ‘metamorphosed,’ that is used in those places in the original text. Why is that so? Is there an important difference between them? And why does the noun ‘metamorphosis’ which is familiar to us never occur in the New Testament? And yet is there some connection between the Transfiguration of Jesus and the Transformation of the Christian?