Robert Richardson was a theologian who lived from 1806 until 1876. He was the personal friend and physician of Alexander Campbell. Richardson was also associate editor and office manager for Campbell's "Millennial Harbinger" for nearly 30 years where he "fairly represented" the views of the early restoration movement. Richardson also wrote a two volume work called the Memoirs of Alexander Campbell. Richardson would also attend Campbell's death and even speak at his funeral.
In the chapter "The Basis of Christian Union" Richardson mentions "those who are Unitarian or Sabellian in faith". Here Richardson makes the reader aware that he is familiar with such non-Trinitarian systems. Richardson presses for strict "language of the Bible" and rejects "all that scholastic jargon". He does not seek to establish an elaborate doctrine of the Trinity anywhere. He simply affirms that "whatever character, office, or relation, is assigned to the Father, to the Son, or to the Holy Spirit in Sacred Scripture." (pg. 65) While speaking of the subject of repentance Richardson notes that in Acts 2:38 the preaching of Peter brought pierced hearts and a command to reform or repent. In his chapter about the Holy Spirit Richardson rightly notes, "The possession of the Spirit is indeed the very evidence of sonship, and the proof that the gospel has been truly believed." (pg. 90)
Around 1852 Richardson compiled Principles of Reformation in order to present a clear and yet concise outline of early restoration beliefs in North America. This work is around 100 pages long and evenly edited by Carson A. Reed. The table of contents include an introduction by Reed followed by a letter to the reader. The nine chapters include titles such as "Distinction between Faith and Opinion"; "The Christian Faith"; "The Basis of Christian Union"; "Patriarchal, Jewish, and Christian Institutions"; "Commencement of the Christian Church"; "The Action and Design of Baptism" and "The Agency of the Holy Spirit in Conversion and Sanctification." as well as others.
Reed notes that in 1856 "a series of conflicts would erupt" causing a segment of the restoration movement to go down a path that Richardson and others did not want to go. He suggests, "Along that path, many of the principles that Campbell, Richardson and other early leaders held highly would no longer be plainly visible on the horizon." (pg. 9) Reed also suggests that Richardson's views were "largely rejected" by southern churches and that "Many of the southern churches took a fork in the river of ideas that fostered a stark rationalism devoid of the Holy Spirit." (pg. 10) Reed also points out that Richardson held Baptism as a sign or seal that does not save. It is a sign that the believer has been pardoned. (pg. 20)
You can also find another review of this work by Douglas Foster here. You can purchase this paperback edition of Principles of the Reformation here. Anyone interested in early North American church history will enjoy the irenic and Christological tenor of Richardson's writings.