"Watch" was a word Christ Jesus used several times. The Master commanded us to watch. He said (Mark 13: 37), "What I say unto you I say unto all, Watch." He also said (Mark 13:33), "Take ye heed, watch and pray."
In "The First Church of Christ, Scientist, and Miscellany" Mary Baker Eddy says (p. 232): "Can watching as Christ demands harm you? It cannot." In the demonstration of the Science of healing, alert watching is one of the first steps. To watch is to note the undercurrents of one's own thought. Through alert watching we can promptly detect the hypnotic suggestions which seem to present themselves to thought. Then we can reject and replace them with the truth. If we are not keeping our watch, if we are not active on the side of Truth, error may enter the door of our thought. To paraphrase an old saying, Satan will always find some mischief for idle minds to do. Spiritual watching helps us to reach the altitude of thought which forestalls the enemy. What is the enemy? It is that which denies God's ever-presence and power.
When one gives a Christian Science treatment what does he do? He knows the truth of God's perfection and of man as His image. He watches to see that there is not one element of error present in his thought. Knowing the truth includes the understanding of the Word of God, the recognizing of the presence and power of God. Treatment is the acknowledgment that Truth is, that it is all-power, all-presence, all-knowing, all-action.