Charles Finney emphasizes the necessity of agreement in heart and spirit for true fellowship, using Amos 3:3 to illustrate that two cannot walk together unless they are in harmony. He explains that mere intellectual agreement is insufficient; true unity requires shared feelings and affections. Finney discusses how differing states of the heart affect perceptions of truth and spiritual matters, leading to discord between saints and sinners. He warns that lukewarmness in faith can lead to dissatisfaction with fervent preaching and spiritual revival, as those whose hearts are not aligned with God will resist the truth. Ultimately, he calls for a transformation of the heart to enable genuine agreement and fellowship in Christ.