In 1 Cor 12, Paul says he wants the brethren "to be quite certain" about the manifestations of the Spirit within them. Paul explains that it is important to clearly understand that nobody is able to claim that Jesus is Lord, except by the Holy Spirit; and likewise, nobody can speak in the Spirit of God against Jesus. The Spirit does not manifest in unbelievers. Next, Paul explains that all varieties of spiritual manifestations in believers are of the "same Spirit" and all serve the purpose of God's work for the common good of the body of Christ. God alone determines how He will manifest His Spirit in each believer. Paul then explains how God unites believers together as one body in Christ to function in harmony. God has arranged the believers as parts of this one body just as He wanted. His design necessitates that the parts interact with cooperation, dependence, honor and respect of each other, and equal concern for each other.