Acts 18

It is evident that as Paul enters a new city our town, he would first teach the Jews in their synagogues. It is interesting that as Paul teaches in Corinth -

"...he reasoned in the synagogue every sabbath, and persuaded the Jews and the Greeks.
5 And when Silas and Timotheus were come from Macedonia, Paul was pressed in the spirit, and testified to the Jews that Jesus was Christ.
6 And when they opposed themselves, and blasphemed, he shook his raiment, and said unto them, Your blood be upon your own heads; I am clean: from henceforth I will go unto the Gentiles." (New Testament | Acts 18:4 - 6)

Paul seemed so frustrated with this congregation, seeing no apparent conversion, that he basically gives up and seems to storm out. But what is interesting that not afterwards we read that Paul -

"...departed thence, and entered into a certain man's house, named Justus, one that worshipped God, whose house joined hard to the synagogue." (New Testament | Acts 18:7)

And then -

"...Crispus, the chief ruler of the synagogue, believed on the Lord with all his house; and many of the Corinthians hearing believed, and were baptized." (New Testament | Acts 18:8)

The point is that in our service we may feel we are getting no where. That our message is not being heard and we are not doing any good. But look at these results because of Paul's diligence, even as he felt a total failure. You never know what good you are doing as you diligently serve.