One aspect of Paul’s ministry is to bring Christians to full assurance of salvation and trust in Christ. Here he speaks specifically of the church at Laodicea, yet it is a need for all Christians. You need to know what you believe. You need to have a full assurance that you are saved. Without knowledge and full assurance of Christ, we are open to attack by what Paul calls plausible arguments. If you are going to grow in your Spiritual life walking with Christ, then you need to be assured of the foundation that it is built upon, your salvation in Christ.
