He returned to Saxony in 1721 and, yielding to family wishes, accepted a public office. Faithful, however, to his youthful ideal of associating with others to sanctify themselves and spread the Gospel, he joined Baron Friedrich Watteville, already his companion at the Halle College, with Rothe, pastor of the Lutheran church in Berthelsdorf, located in his county, and Schäfer, pastor of the nearby town of Görlitz, and formed the “Pact of the Four Brothers” for the stated purpose. At that time some Bohemian Brethren (v.), fleeing from Moravia, had sought refuge in the count’s lands and founded the colony of Herrnhut. Zinzendorf soon realized that among them he could easily fulfill his desire. In 1727 he resigned his public office and settled in Berthelsdorf near Herrnhut, determined to make those emigrants a center of intense Lutheran Pietist and missionary piety. Finding difficulties in the doctrines and organization of the Brethren, he thought it better to revive their Church while preserving in it all that he considered good in Lutheran Pietism, so as to create an “Ecclesia in Ecclesia.” With this aim, he first had himself ordained a Lutheran minister and then, in 1737, a bishop of the Brethren by the two Bohemian bishops, Jablonsky and Nitschmann. From that moment Zinzendorf’s life was intimately united with the work of the “Moravian Brethren” or “United Brethren,” or also “Unitas Fratrum,” names that replaced the old “Bohemian Brethren.” Among them he fostered a spirit of piety and missions, but never wished to impose a confession of faith, although the Augsburg Lutheran Confession remained the basis of their beliefs. He never allowed them to unite with other sects and ensured that they always preserved their special character. Meanwhile, the Lutherans of Saxony, who disliked this “Ecclesia,” obtained from the elector an edict of exile against him in 1736, and he used this time to be consecrated bishop, as mentioned, and to visit various European nations to make his Moravian Brethren known.
In 1739 he traveled to the island of St. Thomas in the Antilles, where a small Moravian mission had already been established, and in 1741 he went to the English colonies. In Pennsylvania he consolidated the Moravian Brethren. After the exile edict was lifted in 1749, he returned to Herrnhut, visiting again Holland, England, and other countries.