Who was the collection in Romans 15:26 for?
The collection mentioned in the passage was gathered by believers in Macedonia and Achaia for the poor saints in Jerusalem. Paul was determined to deliver this contribution to the believing Jews there, ministering to their needs even though the Macedonian and Achaian believers were intensely poor themselves.
Les explains that Paul had been laboring in western Turkey and later in Greece, specifically Achaia and Macedonia. Those regions were mountainous with little opportunity for wealth, so the new believers there were intensely poor. Yet they gave what they had so Paul could take the offering to the poor saints in Jerusalem, who were Jews. Paul was determined to go to Jerusalem first to minister to the believing Jews there, even before his planned journey to Rome and Spain. The contribution was specifically for the poor saints at Jerusalem, as verse 26 states.
For it hath pleased them of Macedonia and Achaia to make a certain contribution for the poor saints which are at Jerusalem.