Galatians 1:6-9 meaning

The Galatians had left Jesus and instead began following a new and twisted version of the gospel; one that is really not another gospel, but a distortion of the one Paul had told them. Paul will debunk this false gospel, which tried to make the Gentiles (non-Jews) adhere to Jewish customs and laws. This false gospel was given to them by men, not God.

To Paul, it doesn't matter who preaches the false gospel (as he tells his audience even if an angel from heaven or any man teaches a false gospel), they should all be rejected by the Galatians.

These specific Jewish leaders, who are now competing against Paul's authority, were leading Gentile believers away from the gospel of faith in Christ, pushing them toward one of religious laws and rules. The competing Jewish "authorities" taught that following the Old Testament Law made a person pure and right before God. (One of the laws they tried to impose on the Gentiles was circumcision, which Paul discusses in Chapter 2 of this book).

Paul is very clear that the false teachers leading the Galatian believers astray should be accursed. "Accursed" is a translation of the Greek word anathema, from which we get our English word anathema. Paul uses the same word in the next to last verse of his first letter to the Corinthian, that Paul writes with his own hand for emphasis: "If anyone does not love the Lord, he is to be accursed" (1 Corinthians 16:22). In this instance, anathema likely carries the meaning of being "excluded" or "avoided". To consider that Paul is saying to the Galatians "throw these charlatans out and have nothing to do with them" would fit well with other biblical teachings regarding false teachers, that they are to be exposed, condemned, and excluded from the company of the saints.