According to some Christian traditions, a second work of grace is a transforming interaction with God which may occur in the life of a Christian. The defining characteristics of this event are that it is separate from and subsequent to salvation (the first work of grace), and that it brings about significant changes in the life of the believer.
Second work of grace Wikipedia
John Wesley, the founder of the Methodist movement, taught that there were two distinct phases in the Christian experience. During the first phase, conversion, the believer received forgiveness and became a Christian. During the second phase, sanctification, the believer was purified and made holy. Wesley taught both that sanctification could be an instantaneous experience, and that it could be a gradual process.
After Wesley's death, mainstream Methodism "emphasized sanctification or holiness as the goal of the Christian life", something that "may be received in this life both gradually and instantaneously, and should be sought earnestly by every child of God."
The Holiness Movement emerged in the 1860s in the USA with the desire to re-emphasize Wesley's sanctification doctrine. Holiness preachers taught that sanctification was an instantaneous experience.
Later, the Pentecostal Movement emerged from the Holiness Movement, teaching that the believer could, in addition to becoming sanctified, receive power from God and the Gifts of the Holy Spirit. In early Pentecostal thought this was sometimes considered to be a third work of grace but over time it has come to be perceived as the major component of the second experience.
In the Holiness movement, the second work of grace is considered to be a cleansing from the tendency to commit sin, an experience called entire sanctification which leads to Christian perfection.
Pentecostalism was born out of the Holiness Movement. Charles Fox Parham and William Seymour were both Holiness Ministers and were seen by their followers as being used by God to restore Pentecost to the Church.
In Pentecostalism, believers are encouraged to seek the Baptism with the Holy Spirit. In most Pentecostal churches, the outward evidence of this experience is the manifestation of the Gifts of the Holy Spirit, most particularly including the Gift of tongues.
Classical Pentecostals distinguish between the manifestation of Tongues at the Spirit Baptism and the Gift of Tongues which is one of the nine gifts of the Holy Spirit found in 1 Corinthians 12:8-10.