"You who are trying to be justified by law have been alienated from Christ; you have fallen away from grace." NIV translation
Paul repeats the fact that trusting in the law instead of the grace of God for salvation is what is meant by "falling from grace".
"But by faith we eagerly await through the Spirit the righteousness for which we hope." NIV translation
Our hope is in the faith that Jesus Christ has repaired our relationship with the Father. The Holy Spirit living in us helps us to wait in confidence of what is to come.
"For in Christ Jesus neither circumcision nor uncircumcision has any value. The only thing that counts is faith expressing itself through love." NIV translation
The law, whether it is about circumcision or anything else, does not apply to those that have accepted Jesus. It is by faith in His finished work on the cross that we are saved and can walk in true freedom.
When we understand that the work is finished and start walking in freedom, then, the love of Christ will simply flow out of us.
"You were running a good race. Who cut in on you and kept you from obeying the truth?" NIV translation
Paul tells the Galatian believers that they were doing well in a race speaking of the fact that they were trusting in the blood of Jesus for their salvation. When you are running in a race and someone cuts in front of you really close it can cause you to stumble and fall. He is asking them the question of who did that to them and tells us that the method they used to get them to stumble was disobeying the truth. Jesus said that He was the Way and the Truth and His blood is the only way that we can be saved. Adding anything to that is disobedience and will make you stumble and fall from grace.
"That kind of persuasion does not come from the one who calls you. 'A little yeast works through the whole batch of dough.'" NIV translation
The preaching that occurs even today where the law is applied to those who have put their faith in Jesus Christ, is not from God but, in fact, is the devil trying to get in and cause confusion. Paul refers to yeast which represents sin throughout the Bible and so is calling this legalism sin. He says that a little bit of the law applied to a believer's salvation corrupts the whole plan of God which is salvation by grace alone.