Spiritually, Presbyterianism embodies the principles of Calvinism and forms the main branch of the Reformed churches. The Westminster Confession (see creed) and the Larger and Shorter Catechism composed by the Westminster Assembly, convened (1643–49) by the British Parliament, provide the doctrinal and liturgical standards for Presbyterian churches. These assert the sovereignty of God and the prime authority of Scripture as guides to church doctrine. The Bible is held to be the rule of government and discipline, as well as faith. Presbyterians accept the sacraments of baptism and the Lord's Supper. They are opposed to state interference in ecclesiastical affairs.