In order to live above the world, an individual must first come into contact with the true gospel of Jesus Christ, for it is the gospel that is the power of God unto salvation (Rom. 1:16). If a person is not first approached with the gospel and is not a true believer in that one gospel, then he cannot, no matter how much he may desire to do so, live above the world in that heavenly bliss of the eternal glory of God, his deliverance from sin, his sealing of the Holy Spirit, his joy of service, and the rapture of living above the earthy and having our citizenship in heaven (Phil. 3:20).
But some in the churches of Galatia had turned from the true, sound, and powerful gospel to another gospel. Since there is no more than one gospel, then turning away from that one and true gospel is the same as turning away from God, Jesus Christ, and the Holy Spirit (to which the word "him" refers in verse six.
This alternate gospel is another (Greek heteros) gospel, or a gospel of a different kind. There is, then, only one kind of the true gospel, not several variations or multifarious gospels of the same kind. Any "other" gospel would be of a completely different kind.
That is why Paul says in verse seven, "which is not another (Greek allos). There can never be another gospel of the same kind as the real and true gospel; thus, Paul warns against any variation of this true gospel. Any variation would be a perversion.
If a gospel of another kind is ever preached, the person by whom it is preached is to be "accursed." This other gospel is one with no power, no cause, no heavenly source, no command for propagation, no blessing of God upon it; so every preacher of the gospel must be very careful to preach the one and only true gospel lest he be accursed by God. See verse eight.
This is such an important concept that Paul repeats himself in verse nine to put forth the forceful and needed pronouncement that anyone who preaches a gospel of another kind will be accursed. Of course, only a lost person would preach such a gospel that is foreign to the word of God. No believer, who has met with the gospel, has been convicted by its power, and has been delivered by faith in it, would dare preach "another gospel." The gospel is the message of the death, burial, and resurrection of Jesus Christ (1 Cor. 15:1-4). Thank God I have met it, have believed it, and have eternal life because of it.