In the middle of Paul’s instruction about how Christians are called to live, he says, “Do not grieve the Holy Spirit.” God’s elect are sealed with the Holy Spirit, the third Person of the Trinity. He applies the benefits of Christ’s redemption, reconciling us to God and to one another. The Holy Spirit unites God’s people and builds up the body of Christ. We grieve the Holy Spirit when we live according to our old way of life for we are opposing His work within the church.