The Apostle Paul was dealing with people who were saying they believed in Jesus as Messiah, and saying they believed He died for their sins, yet they insisted that certain elements of the Law of Moses should be retained as necessary for salvation. These people were called Judaizers, and they included both Jewish people and Gentiles that had converted to Judaism. For the Judaizers, Christ alone was just not enough.
We might think it is demeaning to refer to oneself as a slave or a servant, but in the first century, the slave of a high-ranking official often had more influence and authority than the average free Roman citizen. A servant sent in the name of his master came with conferred authority; therefore, to rebuff the servant was to rebuff the one who sent him. As the servants of Jesus Christ, we have been sent in His name, and there is power in the name of Jesus.
Acts 16 is a powerful chapter illustrating that if we are willing to obey the Holy Spirit, count the cost, and go, then God can do more than we could even ask or imagine. But you gotta start somewhere. This chapter gives a great overview of what is needed to plant a church or start a ministry successfully. Furthermore, it shows us that even in a place that is hostile to the gospel and to the people who proclaim the good news, ministry can be successful.
If Christ is not risen then all our self-denial of carnal pleasures was for nothing. If Christ is not risen then all our prayers were pointless. If Christ is not risen then there is no blessed hope, no heaven, no eternal healing, no restoration of all things, no point, no purpose, and no promise … if … Christ is not risen.