Artimaeus,
By far and away the largest “full gospel” denomination is the Assemblies of God, and I was saved in an Assembly of God church. At the time, I was also regularly fellowshipping at a Baptist coffee house that was open every night except for Sunday and Monday night. Before I even got saved, I could see very clearly that the Assembly of God folks interpreted the Bible differently than did the Baptist folks. And when I got saved, I wanted to know who was right and who was wrong. I especially wanted to know what the Bible really teaches about the Baptism in the Holy Spirit. Therefore I began to study what the Bible says about the Holy Spirit and about baptism. I also began to study what the Assemblies of God teaches about these subjects.
The outcome of this was that I decided that both the Assemblies of God and the Baptists were partially correct and partially wrong. Both groups teach salvation by grace through faith apart from the works of the Law. The Assemblies of God teach that, subsequent to salvation, a second work of grace is to be experienced by faith. They call this “second work of grace” the baptism in/with the Holy Spirit, and they believe that the initial evidence of the reception of the baptism in/with the Holy Spirit is “speaking in tongues.” From this they arrive at the expression, “full gospel,” that is, the good news of both salvation and the baptism in/with the Holy Spirit through faith.
Some individuals in the Assemblies of God do teach that the baptism in/with the Holy Spirit is some kind of a reward for obedience to Christ, but the Assemblies of God, as a denomination, does not teach that at all. The Christian Missionary Alliance church also believes in and teaches a very similar doctrine of the baptism in/with the Holy Spirit, but they do not believe that the initial evidence is always speaking in other tongues. The Church of the Nazarene teaches a similar doctrine but they use very different terminology and they believe that speaking in tongues today is a counterfeit gift. They refer to this “second work of grace” as entire sanctification or the second blessing.
We find this “second work of grace” occurring in the lives of men and women throughout the history of the church, beginning in the Book of Acts, and sometimes the gift of tongues is mentioned, and other times it is not. But this “second work of grace” is seen as a work of grace apart from the works of the Law. Some individuals have experienced what they interpret to be three distinct works of grace, and there are Christian denominations made up of such individuals.
Basically, we are talking about the experiences of Christians and their interpretation of these experiences as they look to the Bible for help in understanding their experiences. They all teach the gospel of salvation by grace through faith, but many of them teach a “fuller” gospel that includes a “second work of grace” through faith.