In his other letters, Paul talks about his evangelism strategy, where he meets his audience in their context. When he first taught to the pagan Galatians, he did not seek to keep himself separate through the ceremonial laws of his upbringing, but showed them that he was a man just like them, a sinner in need of grace. Now he wants them to return the favor by remaining free of the law’s demands because they are free in Christ.
We learn here that Paul was ill in some way when he was with the Galatians, though we don’t know exactly what it was. It might have had to do with his eyes, though some have suggested malaria or epilepsy. Whatever it was isn’t important, but the way the Galatians reacted to it is important. They received him and took care of him in his ailment in spite of the hardship it caused them to do so. But because he was sick and because they took him in, he was able to preach the gospel to them and planted the churches in the region.
The point of bringing this up in the letter is that Paul wants the Galatians to remember the blessing God gave them when they heard his message, and to remember the tender-hearted feelings they had for Paul at that time. He contrasts this with the hard-heartedness that comes from following the legalistic practices of Paul’s opponents. The Galatians know Paul and loved him, and there is no reason for that to change because Paul has not changed nor has his message from God changed. But the attitudes of the Galatians towards Paul have changed, and this causes him anguish and perplexity, which is why he has been using such strong language in this letter. But loves the Galatians still and wishes this were not so.
The pain of discipline and correction comes because You love us too much to leave us in our error.