Galatians 5:11

"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.

Galatians 5:12

"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).

Galatians 5:13

"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.