"Devotion is neither public nor private prayer. Prayers, whether public or private, are particular parts or instances of devotion." These definitions begin William Law’s documentation of his rules of spiritual discipline called, A Serious Call to a Devout and Holy Life. Published in 1728, this book as well as his earlier book, Christian Perfection, had immense influence on John and Charles Wesley. Law was committed to showing how the Christian may increase Christian virtues. Law was a contemporary of Newton, Locke and Woolman. In 1705, he entered Emmanuel College, Cambridge, and became a fellow in 1711. He planned to enter the priesthood of the Church of England but was denied the privilege. Law eventually became a spiritual director for the Wesleys as well as a number of other prominent religious families in England.

Law was known to rise each morning at 5 a.m. and spend time in devotions before breakfast and studying. At 9 a.m. he joined his family in devotion, at which time the Collects and Psalms for the day were offered. For the remainder of the day, he retired to his study to write meditations and to see to the needs of the community. He also devoted himself to the writing of mystical devotional works. Law’s occupation as spiritual leader led him to a breach with John Wesley. Wesley’s conversion under Moravian influences led him to stress the overwhelming importance of justification by faith. Law, on the other hand, according to Wesley, put too much emphasis on the gospel of works.

Wesley did perhaps misinterpret Law’s views, since toward the end of Law’s life his views became very close to Quakerism, with his stress on the "light within." The "light within" is the spirit and power of God dwelling and manifesting itself in a new person .

Law linked the unlawfulness of war with divine love. In his Address to the Clergy, composed between 1760-1761, he speaks against war and military establishment. This was at a time when England was sealing her international empire and Law stood firm that the spoils gained in war were against the virtue of Christ. In the window named for William Law is a shield depicting a symbol for the hand of God. Fire and water, the symbols for death and the life of Christ, respectively, are pictured in the circle. The motif repeated on the diamonds in which an upright torch refers to life and an inverted torch refers to death, exhibits Law’s appeal to the scripture in Ecclesiasticus 15:16-17: "God has set before thee fire and water, stretch forth thy hand unto whether thou wilt. Before men is life and death; and whether him liketh shall be given him."