Because of an infirmity of the flesh (di asqeneian th sarko). All that we can get from this statement is the fact that Paul's preaching to the Galatians "the first time" or "the former time" (to proteron, adverbial accusative) was due to sickness of some kind whether it was eye trouble ( Isaiah 4:15 ) which was a trial to them or to the thorn in the flesh ( 2 Corinthians 12:7 ) we do not know. It can be interpreted as applying to North Galatia or to South Galatia if he had an attack of malaria on coming up from Perga. But the narrative in Ac 13; 14 does not read as if Paul had planned to pass by Pisidia and by Lycaonia but for the attack of illness. The Galatians understood the allusion for Paul says "Ye know" (oidate).