The short answer is that it’s a heresy within the Pentecostal movement that originated in the 1940s. It was pretty serious, almost irrevocably splitting the Assemblies of God in two. Today, it’s fizzled out as any kind of organized movement, but its ideas are still influential, especially in the fringes of the Pentecostal-charismatic world, such as the New Apostolic Reformation, etc.
First, you need to recognize that before the 1940s any reference to “the Latter Rain” almost certainly referred simply to classical Pentecostalism. In the first decades of the 1900s, Pentecostals saw our movement as the “latter rain” of the Holy Spirit (the former rain being the original outpouring in the Early Church). After 1940, however, “the Latter Rain” almost certainly refers to the postwar movement.
This movement was also called the “New Order of the Latter Rain.” The main driver of the movement was the (somewhat correct) belief that the classical Pentecostal denominations had grown spiritually stagnant and were in need of revival and a fresh move of the Spirit. This took on the form of a radical anti-denominationalism, which is one reason there is no “Latter Rain” denomination in existence today.
The “New Order” taught that the gifts of the Spirit (see 1 Corinthians 12:8-10 and Romans 12:6-8) are channeled through church elders, who could impart these gifts to others by the laying on of hands. The Assemblies of God and other classical Pentecostal churches did not believe this was Scriptural. Classical Pentecostals believe that the charismata are not given to people like personal possessions and neither can they be imparted to other people. Spiritual gifts are simply manifested as the Holy Spirit wills. Pentecostals concluded that anyone teaching the imparting, identifying, bestowing, or confirming of spiritual gifts by prophecy and the laying on of hands was incorrect teaching.
The New Order also taught that the church is build on present-day apostles and prophets. This teaching is still seen today in churches that emphasizes the complete restoration of the five-fold ministry including offices of apostles and prophets. While classical Pentecostals believe in contemporary prophecy, they had never formalized any kind of prophetic office; people simply prophesied when led to by the Holy Spirit without claiming any kind of prophetic office. Likewise, classical Pentecostals had always taught that the contemporary apostolic ministry within the church was one of taking the gospel to new lands. We did not see it as any kind of formal leadership structure for today.
The Latter Rain also had a theology that rejected a pre-tribulation rapture. Instead, they believed that in the last days a class of “supermen” would emerge that would essentially be “manifested sons of God” exercising all of the power that Christ did while on earth. This last teaching in particular was deemed as heresy.
