Some have confessed difficulty with these verses, especially with the words "another gospel: Which is not another." This problem finds resolution in an understanding of two distinct Greek words which unfortunately, are both here translated as "another" in this passage.
In verse 6 Paul uses the Greek word, heteros, which implies something of a totally different sort altogether-- something diametrically opposed to the one to which it is compared. But in verse 7 he uses the word allos, which implies a comparison of two items of the same sort. The thought might be conveyed as follows: "You are removed from the true gospel of the grace of Christ unto a totally different belief system, which is not simply a similar but legitimate expression of the true gospel. Instead, it is quite opposite to the truth." Paul goes on to teach that this "different" gospel is a perversion of the true gospel, and instead of bringing peace, it brings about a troubling of the mind.
The primary theme of the entire book of Galatians is salvation by grace through faith in Christ, as opposed to salvation by works and law. "No man is justified by the law in the sight of God. . . . The just shall live by faith" (3:11). This marvelous good news had been denied by many in the Galatian church, but Paul had received the message of grace "by the revelation of Jesus Christ" (1:12). Any mixture of works with grace constituted a perversion of God's plan, and any who would teach such perversion warranted strong condemnation from Paul. "If any man preach any other [from the Greek word para, meaning contrary] gospel unto you than that ye have received, let him be accursed" (1:9). JDM