"I am confident in the Lord that you will take no other view. The one who is throwing you into confusion will pay the penalty, whoever he may be." NIV translation
Paul reassures the Galatian believers that he has confidence that they will stand on the gospel of grace which he preached. He also explains that the one that is trying to put them back under the law will answer for his actions. This reminds us of the responsibility of leaders in the body of Christ and the fact that they must be grounded in the gospel and not traditions.
"Brothers, if I am still preaching circumcision, why am I still being persecuted? In that case the offense of the cross has been abolished." NIV translation
As Saul (before Paul came to Christ) he preached circumcision (the law) and even hunted down Christians. The religious leaders liked him then but now that he was preaching about the grace of God they did not like him. When he talks about the "offense of the cross" he is talking about the fact that, to people that are trying to teach the law for salvation, the idea that Christ paid for our sins on the cross is offensive to them. It is the same even today when you speak about the radical grace of God. Many will still be offended by the fact that obedience to the law cannot bring salvation and the grace of God brings freedom from the law.
"As for those agitators, I wish they would go the whole way and emasculate themselves!" NIV translation
Paul says that he wishes that the Judaizers would go the whole way and trust completely in the law instead of compromising the gospel of grace.
That is what Jesus was saying to the church in Laodicea when He said that He wished they were either hot or cold (see Revelation 3:15 & 16).
"You, my brothers, were called to be free. But do not use your freedom to indulge the sinful nature; rather serve one another in love." NIV translation
Because of God's grace, we are free from sin and its penalties and that is the freedom that we have. Once we are free, we can choose to serve others in love or we can choose to focus on ourselves and what we desire. Paul urges the Galatian believers to focus on serving others out of the love that has been shown to us through Jesus Christ.