What did I learn from that trip in Costa Rica?

The foremost thing would be that the Gospel is central in the life of both the unbeliever and also for the believer. Paul wrote in Romans 1:17 “So I am eager to preach the gospel to you also who are in Rome.” Paul wrote this to Christians believers, not unbelievers. Our tendency is to give an unbeliever just enough of the gospel to get him or her to pray a prayer to receive Christ as His personal Saviour. Then we immediately put the gospel on the shelf, and go on to the duties of disciples. The problem is that many believers have only a very elementary knowledge of the gospel. In fact Paul always preach the gospel to believers then apply the gospel to their lives.