Mary Baker Eddy designates Principle as one of the synonyms for God because the meaning of Principle as fundamental basis, as that from which all that is real proceeds, as unlimited power which maintains the operation of divine law, rightly describes this aspect of Deity.
The operation of divine Principle maintains creation in undeviating harmony and unchanging perfection. Christian Science teaches that the understanding and utilization of God's law bring to light man's unchanging harmony. It teaches further that the material body is but the outward expression of a mistaken material concept of man, and that any sense of inharmony or imperfection has no reality, power, or history in the realm of Principle, or divine Mind, God.
Since the human body is constructed by mortal mind of false beliefs objectified as forms of matter, discords are not primarily in the body, but in the human mind which has accepted these false beliefs. To attain harmony, we do not deal with the body, but with the truth that Principle and its idea constitute reality. Then false beliefs and their effects are driven out of consciousness, and a harmonious body results.