In verse 11 Paul reminded them of his personal life. Some have suggested that he was speaking here of having poor eyesight. Some have suggested that his eye sight problems were the after effects of his being blinded by God on the road to Damascus prior to his salvation. That seems strange to me because the Bible tells us that Ananias was sent to Saul while he was in Damascus to pray for him that he might received his sight. When God healed someone in the Bible they were healed. They did not suffer from the effects of their infirmity after they were healed.
We do know that at the end of some of his other epistles, he mentioned that someone else had written the letter as Paul would dictate it to them. Paul was directed by God to mention that he had written this letter himself.
In verse 12 Paul reminded them that those who were pressing them to be circumcised were acting in the flesh. The Jews would already have been circumcised. However, the Judaizers were trying to convince the saved Gentiles that their salvation was not complete without circumcision. The word translated as “constrain” means “to necessitate.” Paul was directed by God to remind and also to urge the saints to follow the truth. The Holy Spirit indwelt them. He would guide them if they would let Him. If they chose to follow the lies, they needed to understand, that was acting in the flesh.
Jesus had taught the disciples that in following Him the world would hate them. The Judaizers were persecutors. They knew that if they would trust God they would face persecution. They sought to keep others from the truth. They did not want to identify with the cross of Christ. They were short sighted in their thinking and would rather spend eternity in hell, rather than face a short time facing persecution in the present. The Judaizers were blinded because they were lost. The Galatian saints were saved. They had the Light of the World in their hearts. They knew better than what they were toying with.
Paul stated that the Judaizers did not keep the law. They were circumcised, but they did not obey the other laws. They had a false god and a false gospel. Jesus had often exposed the Pharisees for their hypocrisy. The Judaizers were similar to the Pharisees. The Judaizers tried to force the Gentile saints to be circumcised so that they could boast of how they had brought the saints into submission to their false teaching.
True saints do not blindly follow others. True Christianity is not a blind faith. Hebrews 11 tells us:

Hebrews 11:1 Now faith is the substance of things hoped for, the evidence of things not seen.

True faith can be examined and it is founded in the Word of God.
Paul contrasted the Judaizers with himself. He did not glory in the flesh. He knew that would be foolish and wicked. The truth was important and he chose to glory in the cross of our Lord Jesus Christ. He reminded the saints that the Lord Jesus Christ was “our” Lord Jesus Christ. They were saved. They needed to remember that. He was not trying to convince lost people they were saved. He was reminding the saints of how they were saved.
The apostle Paul stated that the world was crucified to him. He had no attraction to the world. He was not tempted to go back to his former life. There was nothing in the world for him, nor for any true child of God. The devil tries to make the world look enticing. Many Christians fall for the glimmer of the world. However, they soon find out it is not worth it.
The true child of God has a treasure that far outweighs anything the world has to offer. When the true child of God lives in the light of God’s Word, he or she has something to offer the world. When a child of God tries to love the world, they have nothing to offer the lost. That is why the New Evangelical crowd is worthless. They have the noise of worldly music. They like a perverted gospel that cannot save and is designed to make a lost sinner feel good about their sin. It is sad that so many are enticed to follow that lie, but the true child of God cannot go that way. It is contrary to the new nature.
In verse 15 we are reminded that in Christ circumcision is not of any value. Uncircumcision is also nothing. A person is not saved by circumcision. A person is also not condemned because they are uncircumcised. Notice that Paul reminded the saints that they were new creatures in Christ. That is the reality. Paul was not directed by God to tell the Galatian saints something that was not real. He was not puffing them up with empty words. He was reminding them of what Jesus Christ had done in their hearts and lives. They had been changed by turning to God in repentance and trusting in the Lord Jesus Christ alone for salvation.
The devil is the great deceiver. He works hard to try to keep the lost, lost. He also works hard to try to keep the saved from living in the light of who God has made them from the moment of salvation. He cannot win with the saved, but he thinks he can. As you read the writings of the apostle Paul, you find that he was led by God to remind the readers over and over again of what they must be in Christ. His was not a message of “easy believism” that is so common today. His was a message that confronted sin and that showed what must be there if a person was truly saved. God is not trying to chase people away.
We are often told that if we are not careful we will turn people away from the Gospel. I received an email this week of a man who is travelling across the country with what he believes to be his calling. He says he has developed a way to get people interested in reading the Bible. He greatly lacks discernment. He does not understand that God draws people to Himself. God, the Holy Spirit stirs in the heart of the lost to draw them to repentance and salvation. This man is like most professing Christians who have never stopped to think about verses like II Timothy 3:16-17.

II Timothy 3:16 All scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness:
17 That the man of God may be perfect, throughly furnished unto all good works.