The Lord reveals his glory in the presence of chosen witnesses. His body is like that of the rest of mankind, but he makes it shine with such splendor that his face becomes like the sun in glory, and his garments as white as snow.
The great reason for this transfiguration was to remove the scandal of the cross from the hearts of his disciples, and to prevent the humiliation of his voluntary suffering from disturbing the faith of those who had witnessed the surpassing glory that lay concealed.
With no less forethought he was also providing a firm foundation for the hope of holy Church. The whole body of Christ was to understand the kind of transformation that it would receive as his gift. the members of that body were to look forward to a share in that glory which first blazed out in Christ their head.
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Pope Saint Leo the Great from a homily