I had to reproduce my own copy of the Marrow of True Justification from microfilm; so, I'm really looking forward to this SGCB reprint, which will be much more readable and will serve as a fine working/study volume.
Here's a brief theological biograpy of Benjamin Keach.
Benjamin Keach (1640-1704) was born to John and Feodora Keach. When he was fifteen years old (1655), Keach converted to Christ under the ministry of Matthew Mead, an Anglican minister, who was a warm evangelical Calvinist free from the taint of antinomianism. But due to the fact that Keach firmly held to believer’s baptism and liberty of conscience, he sought baptism by immersion under the ministry of John Russel, a General (Arminian) Baptist pastor. In 1558, when he was sixteen years old, Keach's church set him apart for the ministry. Though he held Arminian notions of the will for a time, Keach soon became convinced of the Calvinist doctrine of the will, probably sometime after 1668 when the Southwark church installed him as pastor. The doctrines of justification and the covenant of grace undergirded Keach's Calvinist convictions about the will. Austin Walker notes that Keach embraced the Calvinistic doctrine of the human will by coming to a clearer understanding of the doctrine of justification as articulated in John Saltmarsh’s book, Free Grace: or the flowings of Christ’s blood freely to sinners, which was published in 1645. Though Saltmarsh, who was apparently an antinomian, was Keach’s first instructor in these things, Keach himself never embraced antinomian convictions, but always affirmed that both sinners and saints are responsible to obey all of God’s commands. Throughout his career, Benjamin Keach strenuously maintained a defense of warm orthodox Calvinism.
 For more biographical information on Keach, see William Cathcart, ed., Baptist Encyclopedia, vol. 1 (Philadelphia: L.H. Everts, 1881), s.v. “Keach, Rev. Benjamin,” 637-638; Thomas Crosby, The History of the English Baptists (London: 1739), vol. ii, 185-209; vol iii, 143-147; vol. iv, 268-314; Michael A.G. Haykin, Kiffin, Knollys, Keach: Rediscovering our English Baptist Heritage (Leeds: Reformation Today Trust, 1996), 82-103; Thomas J. Nettles, The Baptists: Key People Involved in Forming a Baptist Identity, vol. 1. (Fearn, Ross-shire, Scotland: Christian Focus Publications, 2005), 163-193; Adam A. Reid, “Benjamin Keach, 1640,” Baptist Quarterly 10 (1940-1941): 67-78; James Barry Vaughn, “Benjamin Keach” in Timothy George and David Dockery, eds., Baptist Theologians (Nashville, TN: Broadman Press, 1990) 49-76; Austin Walker, The Excellent Benjamin Keach (Dundas: Joshua Press, 2004), 1-423; Walter Wilson, The History and Antiquities of the Dissenting Churches, vol. 4 (London: 1808), 243-252; Hugh Wamble, “Benjamin Keach, Churchman,” Quarterly Review (April-June 1956): 29-34.
 Walker, The Excellent Benjamin Keach, 47-48. See also Matthew Mead, The Almost Christian Discovered, or the False Professor Tried and Cast (London, 1675. Morgan, Pennsylvania: Soli Deo Gloria, 1993).
 Ibid., 41.
 Nettles, The Baptists, vol. 1, 163.
 Ibid., 338. Keach became the pastor of the Southwark church after the Clarendon Code had come into full effect by 1665. This code made it enormously difficult to minister as a dissenting minister and was the cause of much persecution.
 Walker, The Excellent Benjamin Keach, 50-51.