Why does Paul mention the number of days that he stayed with Peter?
Galatians 1:18 (ESV)
18Then after three years I went up to Jerusalem to visit Cephas and remained with him fifteen days.
Paul mentions the number of days that he was with Peter in order to affirm that the time he spent in Jerusalem was relatively short.1 He does this to affirm that he was not dependent on Peter for the gospel (or the churches in Jerusalem for his commission to preach).2
18 Then after three years I went up to Jerusalem to visit Cephas and remained with him fifteen days.