Who were the saints in Jerusalem that Paul ministered to?
The saints in Jerusalem were the believing Jews there, described as the poor saints at Jerusalem. Paul was determined to go first to Jerusalem to minister to them, taking the contribution given by the believers in Macedonia and Achaia so their poverty could be relieved.
Les explains that Paul had been constantly looking to go to Rome and then west to Spain, but first he was determined to go to Jerusalem to minister unto the saints, that is, the believing Jews there in Jerusalem. Those saints are also called the poor saints at Jerusalem. The believers in Achaia and Macedonia—new believers in the rural, mountainous parts of Greece who were intensely poor—gave of what they had so Paul could take the offering to the poor Jewish saints in Jerusalem. Paul did not know he would end up going to Rome as a prisoner.
But now I go unto Jerusalem to minister unto the saints.