The exercise of the presence of God consists partly in the operation of the intellect and partly in the operation of the will. The intellect represents God as present, and the will unites the soul to God by acts of adoration, of love, of humility and the like. In regard to the intellect, the presence of God may be practised in various ways.
Carissimi; Today’s Mass: St Erconwald, Bishop & Confessor
What valour does not the soldier show when fighting Under the eyes of his Sovereign! The sole thought that his prince by whom he shall be punished or rewarded is present, inspires him with great courage and strength. Hence, if men only reflected that God was looking at all their actions, they would do all things well, with a pure intention, without seeking to please any one but God, and without any regard to human respect.
The Practice of the presence of God is justly called the foundation of the spiritual life. The spiritual life consists of three things: the avoidance of evil, the practice of virtue, and union with God. The practice of the presence of God preserves the soul from sin, leads it to virtue and unites it to God in holy love.