This movement should be distinguished from the loose grouping of churches unofficially referred to as the Plymouth Brethren (or Christian Brethren) and its related movements and sects. The Plymouth Brethren originated in the British Isles, while the Brethren and Pietist Churches have their roots in Germany.
An international religious revival began in Germany in the late 1600s with the writings of Jakob Philip Spener (1635-1705). Spener decried the barren intellectualism, theological factionalism, and general ineffectiveness of the Protestant churches of his day.
He called for a new type of Reformation that would complete the promise of Luther’s Reformation. Luther had reformed the church doctrinally and liturgically; Spener wanted to reform is morally and spiritually.
He called for pastors to find ways to make the doctrine of the priesthood of all believers effective in the hearts and souls of the people. To do this, he proposed that pastors form small groups of believers to meet for study, prayer, and mutual encouragement. The staples of modern church life, such as Sunday School, youth fellowshipo, and women’s circle meetings, grew out of this idea.
Also, Spener urged pastors to leave polemics aside and concentrate on edifying preaching that could transform individuals from sinners to laborers for God.
This “religion of the heart” spread throughout Protestant German and profoundly influenced John Wesley’s (1703-1813) early Methodist movement. When Pietism, as it was called in germany, came to the U.S. in the 1740’s, it helped to fuel the First Great Awakening.
Many Pietist bodies use the name “Brethren” in various forms. For them, the church is primarily a company of brothers and sisters in Christ joined together by the Holy Spirit for mutual edification.
The inner spiritual life, piety, is cultivated in prayer and study of Scripture and through association with fellow believers.
For most Brethren, the local church is central, but they are often bound in close-knit national communities. The church claims their primary loyalty and is understood more as a community of people who love God and one another than as part of an organization or a body that formulates doctrine.
Brethren do not emphasize rigid doctrinal standards; rather, the Spirit of God within each person, binding them together in love, takes precedence for them.
They usually live a simple, unadorned life.
In their early decades in Europe and the United States, most Brethren were separatists from the state and conventional churches. While not manifesting a judgmental attitude, they devoted themselves to a moral purity that set them apart from other Christians as well as from general society.
– Source: Handbook of Denominations in the United States
Frank S. Mead and Samuel S. Hill, Abingdon Press, Nashville, 11th edition (May 1, 2001) Pages 157-158