"I am amazed that you are so quickly deserting Him who called you by the grace of Christ, for a different gospel; which is really not another; only there are some who are disturbing you and want to distort the gospel of Christ.
But even if we, or an angel from heaven, should preach to you a gospel contrary to what we preached to you, he is to be accursed! As we have said before, so I say again now, if any man is preaching to you a gospel contrary to what you received, he is to be accursed!" Galatians 1:6-9 NASB
One of the most potent and pervasive messages Satan has used to confuse mankind, and keep billions content in their lostness is "there are many ways to God." It is a classic example of the truth of Proverbs 14:12: "There is a way which seems right to a man, But its end is the way of death." It is the natural assumption with which we are born: "with billions of people on the planet who do not believe upon the Lord Jesus Christ for salvation, surely God accepts the sincere worship of those who are trying their best to please Him. Thus, there are as many paths to God as there are people...right?"
Yet the Lord Jesus declared, "I am the way, the truth, and the life; no ones comes to the Father but through Me," (John 14:6). John the Baptist echoed the Lord Jesus' claim by saying, "He who believes in the Son has eternal life; but he who does not obey the Son will not see life, but the wrath of God abides on him," (John 3:36).
And then Paul, confronted by the risen Christ on the road to Damascus, proclaimed the same grace of Christ to the Galatians, resulting in the salvation of many. Paul then stayed in the area several years, discipling the new converts, teaching them the implications of their salvation. Yet, through the intimidation and lies of the Judaizers, the Galatian believers were victimized by the lure of legalism. They were enamored with the trappings of Judaism's regulations, restrictions, and rituals, rather than the simplicity of growing in grace by faith.
The tangibles (strict diet, rites such as circumcision, prayer schedule, special clothing), were pleasing to the flesh, bolstering the thought that surely externals can complete what internals began. Besides, such heresy isn't all that serious, is it?
With apostolic authority unique to those whom the Lord Jesus called as such, Paul pronounced anathema upon all distortion of the gospel of grace. As John MacArthur notes, "(the term) refers to devoting someone to destruction in eternal hell," (cf. Romans 9:3; I Corinthians 12:3; 16:22). Twice Paul declares this judgment upon "any man preaching to you a gospel contrary [other than, more than] to what you received" (v. 9).
Taking God seriously requires taking the message of salvation by grace, through faith, without works, forever, seriously. Although this truth cuts across the "anything you believe is ok, as long as you're sincere" philosophy of the world, and counters the mixing works with grace (works righteousness) of many "churches," the Bible's clarion call to doctrinal purity remains fixed.