When God formed man at the beginning, He suspended the things of nature on his will, and made an experiment by means of one commandment. For He ordained that, if he kept this, he should partake of immortal existence; but if he transgressed it, the contrary should be his lot. Man having been thus made, and immediately looking towards transgression, naturally became subject to corruption. Corruption then becoming inherent in nature, it was necessary that He who wished to save should be one who destroyed the efficient cause of corruption. And this could not otherwise be done than by the life which is according to nature being united to that which had received the corruption, and so destroying the corruption, while preserving as immortal for the future that which had received it. It was therefore necessary that the Word should become possessed of a body, that He might deliver us from the death of natural corruption. For if, as ye 
say, He had simply by a nod warded off death from us, death indeed would not have approached us on account of the expression of His will; but none the less would we again have become corruptible, inasmuch as we carried about in ourselves that natural corruption. -- Leontius against Eutychians, etc., book ii.