1 corinthians 2: the natural (Psychikos) vs spiritual (Pneumatikos) man

In the last chapter, some members of the church were ranking their preachers, taking sides. Paul said that when he began to preach to them (Acts 18), he was afraid that they would not accept the message:

3-5 I was unsure of how to go about this, and felt totally inadequate — I was scared to death, if you want the truth of it—and so nothing I said could have impressed you or anyone else. But the Message came through anyway. God’s Spirit and God’s power did it, which made it clear that your life of faith is a response to God’s power, not to some fancy mental or emotional footwork by me or anyone else.

Now, imagine a greater preacher of today that thinks highly of himself. Would he say such a thing? Imagine a gentile world, full of false gods, with philosophers that saw life in different ways. Now, imagine Paul with the message that Jesus is the Messiah that was crucified for our sins and resurrected from the death. Certainly that this message would sound foolishness to the natural men and yet, Paul says that this is the wisdom from the Lord, the wisdom that the spiritual men received from the Spirit. 

1 corinthians 1: Is the gospel foolishness?

Paul writes 1 Corinthians in response to a letter from Chloe’s family and a letter that the Corinthians sent to Paul asking many things. The beginning of the church is written in Acts 18, 3 years before this letter. Corinth was a great port city, gathering people from many places of the world, with their different gods. At that time, the Greek culture, Greek wisdom was very appreciated. It was common to argue about ideas and people and choose one. That is what was happening in Corinth when they were picking sides: Paul, Peter, Appolo and the Messiah. When they were taking sides, they were proud about their own wisdom, their capacity to choose the best ideas and the best people. In this scenario, Paul remembers that they were not outstanding people and even so, they were chosen by God. To be chosen by the Lord to see the beauty of the cross is far more important than to boast about oneself. Paul writes:

18-21 The Message that points to Christ on the Cross seems like sheer silliness to those hellbent on destruction, but for those on the way of salvation it makes perfect sense. This is the way God works, and most powerfully as it turns out. It’s written,
I’ll turn conventional wisdom on its head,
I’ll expose so-called experts as shams.
So where can you find someone truly wise, truly educated, truly intelligent in this day and age? Hasn’t God exposed it all as pretentious nonsense? Since the world in all its fancy wisdom never had a clue when it came to knowing God, God in his wisdom took delight in using what the world considered stupid—preaching, of all things!—to bring those who trust him into the way of salvation.

Galatians 6: A healthy church

Paul wants that the Galatians be a healthy church where they follow the law of Christ: "Bear one another’s burdens", where one help another when falls (in temptation). Following Galatians 5, this is possible when each sees himself as a beggar that is set free to love, trusting in Jesus sacrifice. Indeed, Paul says:

14-16 For my part, I am going to boast about nothing but the Cross of our Master, Jesus Christ. Because of that Cross, I have been crucified in relation to the world, set free from the stifling atmosphere of pleasing others and fitting into the little patterns that they dictate. Can’t you see the central issue in all this? It is not what you and I do—submit to circumcision, reject circumcision. It is what God is doing, and he is creating something totally new, a free life! All who walk by this standard are the true Israel of God—his chosen people. Peace and mercy on them!

A church will not be healthy when one trust in his own merits, such as circumcision or any other religious deed such as paying the tithes. This leads to people that compare themselves feeling superior to others. 

Galatians 5: the free beggar

The beggar can´t survive by himself. The Christian is the beggar who is aware that he can't trust in his own works to get near the Lord. The Christian knows that he can only trust in the cross - Jesus died to him and that's why the Lord accepts him. When the beggar is aware of his condition, and aware of what he has received, he is free of himself. He is free for loving others. The Spirit moves in him producing love, peace, joy, patience; but when he trusts in his own works (ex: circumcision), he begins to exalt above others. Instead of loving, he competes with others trying to be some imaginary race. He hates others. He wants to be the number 1.
Am I aware of my condition? 

Galatians 4: The Creator is the "Papa/Father" to those who has Jesus.

 Paul said to the Galatians:
4-7 But when the time arrived that was set by God the Father, God sent his Son, born among us of a woman, born under the conditions of the law so that he might redeem those of us who have been kidnapped by the law. Thus we have been set free to experience our rightful heritage. You can tell for sure that you are now fully adopted as his own children because God sent the Spirit of his Son into our lives crying out, “Papa! Father!” Doesn’t that privilege of intimate conversation with God make it plain that you are not a slave, but a child? And if you are a child, you’re also an heir, with complete access to the inheritance.

Paul said that the Galatians were kidnapped by the Law, but Jesus came to redeem them; so they don't have to (or must not to) apply the ceremonial law (make the circumcision) to them. They became children of the Lord, and they now have the Spirit of Jesus into their lives crying "Papa!" to the Lord.
Paul remembers how the Galatians were friendly to him, but now, due to the Judaizers, he feels that their relations is colder. He said that the Judaizers want them to become slaves when in fact they were the slaves (of the Law).

Galatians 3: Who are the people of the Lord? trust vs ceremonial law

The Galatians believed in Jesus. There were signs that the Spirit was with them; however, they received Christian-Jews who told them that the ceremonial law, the circumcision, was necessary to be seen as the people of Lord. Why did they listen to these Christian-Jews? Because they were descendants of Abraham, because they were the people that received Moses and the prophets. Paul used the Old Testament to argument that the Galatians are in fact the people of the Lord not by the law but by trusting in Jesus because:
Genesis 15:6 - Abraham was saved (seen as just by the Lord) by faith before the Law.
Genesis 12:3 - The promise to Abraham included all nations.
Deuteronomy 27:26 - The Law demands perfection (and we fail).
Habakkuk 2:4 - The righteous live by trusting God.

Therefore, the Galatians don't need to be circumcised to be accepted by the Lord. In fact, they were already accepted by the Lord when they trusted in Jesus, and it was notorious that the Spirit was with them.

5-6 Answer this question: Does the God who lavishly provides you with his own presence, his Holy Spirit, working things in your lives you could never do for yourselves, does he do these things because of your strenuous moral striving or because you trust him to do them in you? Don’t these things happen among you just as they happened with Abraham? He believed God, and that act of belief was turned into a life that was right with God.

Galatians 2: The beauty of the cross

Paul says that he has authority given by Jesus. He was not ordained by anyone. Thus, when he says that salvation comes from Jesus, and Jesus only; he is claiming that he has authority to say so. He also says that no one can be saved by keeping the law and the Jews know it very well because they are unable to keep all the law. Besides, when someone says that although Jesus saves, it is still necessary to keep the law for salvation, he is not seeing the beauty of the cross, he is not seeing the beauty of the Jesus' sacrifice.
By the cross, Jews and gentiles can live together, in harmony.
By the cross, we are free to be ourselves before the Lord; we don't need masks because we are accepted by Jesus and not by what we do.
Paul rebuked Peter when he disguised that he behaved more like a Jew in front of the Jews and gentiles. For Paul, Peter was in fact distorting the gospel, he was an hypocrite because he knew that Jews and gentiles could live in harmony by the cross. Peter's behavior would send a message that circumcision is important and causes division. 

Paul says:

19-21 What actually took place is this: I tried keeping rules and working my head off to please God, and it didn’t work. So I quit being a “law man” so that I could be God’s man. Christ’s life showed me how, and enabled me to do it. I identified myself completely with him. Indeed, I have been crucified with Christ. My ego is no longer central. It is no longer important that I appear righteous before you or have your good opinion, and I am no longer driven to impress God. Christ lives in me. The life you see me living is not “mine,” but it is lived by faith in the Son of God, who loved me and gave himself for me. I am not going to go back on that.