His theology was and still is one that haunts all of us who care for the gospel today.
His views were rightly opposed by Andrew Fuller in the 1700's and by other gospel centered saints because he wrongly came to the idea that all one needs to do to be saved is mentally affirm that Christ died and arose again. Historical knowledge was what saved not a personal faith in the actual work of Christ.
His views undercut the essence of the gospel that teaches salvation is when a man or woman personally believes or trusts in Christ as Lord and Savior (a set of terms used about 100 plus times in the NT).
We can indeed praise him for his desire to try and go back to the Bible as his course for building a pure theology. To that end we can all praise God for his desire and effort to be a biblicist. Not enough today desire to do that.
However, in the end we cannot claim his type of message as it undermines the idea of salvation by grace through a faith that is in Christ as the one who actually does deliver us from our sins (Matt. 1:21).
He and the movement he led actually reduced the gospel to the idea that simply believing the historical facts of Christ's death and resurrection saved you, instead of a personal trust and faith in Christ to actually deliver you from sin.
A modern day advocate of that developed under the leadership of Zane Hodge (20th and 21st century). His views, which were in root form Sandamanian, even went to another step to deny that one even needed to understand the cross. He taught one could simply believe in Jesus and yet know nothing about this Jesus that one believed in and that was sufficient to save. His views have been labeled the
crossless gospel.
Hodge has said:
“I know that I trusted Christ for salvation before I realized that Jesus was the Son of God.” I was surprised because I had never heard anyone say this before. But I did not quarrel with that statement then, nor would I quarrel with it now. [Zane C. Hodges, “How to Lead People to Christ, Pt.1,” Journal of the Grace Evangelical Society 13 (Autumn 2000): 5.]
Neither explicitly nor implicitly does the Gospel of John teach that a person must understand the cross to be saved. It just does not teach this. [Zane C. Hodges, “How to Lead People to Christ, Pt.1,” Journal of the Grace Evangelical Society 13 (Autumn 2000): 7.]
The simple truth is that Jesus can be believed for eternal salvation apart from any detailed knowledge of what He did to provide it. [Zane C. Hodges, “How to Lead People to Christ, Pt.2,” Journal of the Grace Evangelical Society 14 (Spring 2001): 12.]
All of these views are logical extensions of what Robert Sandeman started. Historical affirmation of a fact was enough in his view for one to be saved. Now, disciples of that line of thought believe that simply knowing the name of Jesus as a fact is enough to make one a true believer.
Theologian Tom Stegall has properly and succinctly shown this view to be a damning and radical departure from the simple message of Christ and the cross, which the apostles taught. He says:
Despite Hodges’ personal dislike for this cross-centered approach to evangelism, the apostle Paul, writing under the inspiration of the Holy Spirit, certainly had no such antipathy. He summarized his Gospel presentation as centered in the cross-work of Jesus Christ. In 1 Corinthians, Paul repeatedly made the summary statement that his message “to those who are perishing” was “the message of the cross” (1 Cor. 1:18). And though he initially preached other Gospel truths to the Corinthians besides the cross-work of Christ (1 Cor. 15:3-4), in recounting the message of his initial evangelization of them, he did not hesitate to summarize by saying, “And I brethren, when I came to you. …determined not to know anything among you except Jesus Christ and Him crucified” (1 Cor. 2:1-2). This was also how he summarized his evangelistic message towards all Jews and Gentiles, not merely the Corinthians, since he boldly declared, “we preach Christ crucified, to the Jews a stumbling block, and to the Greeks foolishness” (1 Cor. 1:23). It was through the “foolishness” of this “message preached”—this “message of the cross” (1:18)—that God would “save those who believe” (1 Cor. 1:21).
A brilliant mind and outgoing personality he indeed did have, along with a good work ethic. To that we may praise God. But as for his teachings that is another story all together. His views are nothing honorable for the cause of the gospel for which our Lord bled and died and to which we are commissioned to share with others as we urge and plead with them to be reconciled to God through the belief in Christ who died to pay for their sins.
Dr. Allen
Robert Sandeman, was a student at the University of Edinburgh where he met John Glas (1695-1773). John Glas believed in the restoration of the New Testament church and he began in repudiating human creeds, human names and human doctrines. Robert not only had a brilliant mind but an outgoing personality. About 1755 he joined John Glas and together they set out to "restore primitive New Testament practices." Both believed in church autonomy, observing the Lord's Supper on the first day of the week, that faith comes as a result of evidence or testimony, and the possibility of restoring the New Testament church. Robert Sandeman came to America in 1763 where he established the Lord's church in Boston, Massachusetts, Portsmouth, New Hampshire, and Danbury, Connecticut. He settled in Danbury and remained there until he died on April 2, 1771 at the age of 53 years. 
