A false gospel is a gospel that gives a false hope.
It does so by preaching a false Christ.
There are various ways of preaching a false Christ.
Arminians preach a Christ who does not actually save, that puts salvation into the believer’s own hands, emphasizing the decision to follow Christ otherwise Christ cannot actually save them. It is another form of neonomianism.
Hyper-evangelism makes the doctrine of Christ’s substitutionary death for sinners the object of saving faith rather than Jesus Christ Himself.
Roman catholics put their trust in their institution to save them with its sacraments that it teaches are essential to salvation.
Unitarians preach an inadequate Christ. Similarly the Jehovah’s Witnesses.
John Gerstner asserts that “No matter how many other important truths it proclaims, it cannot be called Christian
if it empties Christianity of its essential message.” What is that essential message? “What is indisputably, absolutely, and uncompromisingly
essential to the Christian religion is its doctrine of salvation.” Wrongly Dividing the Word of Truth: A Critique of
Dispensationalism, John Gerstner (1991:150).
It might seem harsh and unchristian to criticize the theology of various streams of Christian thought, and there are those who think that doctrine divides and should be kept to a minimum. However, the apostle Paul sets the tone:
“I marvel that you are so soon removed from him who called you into the grace of Christ unto another gospel, which is not another; but there are some who trouble you and would pervert the Gospel of Christ. However, though we, or an angel from heaven, preach any other gospel unto you than this which we have preached unto you, let him be accursed.
Galatians 1:6-9
As we said before, so say I now again, If any man preach any other gospel unto you than that you have received, let him be accursed.”
There is only one Gospel, one Jesus Christ but there are multitudes of counterfeits. Can you tell the difference? Do you care? Do you see the danger of a counterfeit? Jesus continually warned against charlatans preaching false Christs, so you need to be on your guard by reading His own words in the four Gospels in the Bible – Matthew, Mark, Luke and John.
You should pray to God that His Holy Spirit will not allow you to deceive yourself on this important matter. By definition, a person that is deceived does not know it until it is pointed out to them.
This is where mature Christians can help you, but many old Christians are also deceived because they have not used the Bible to correct themselves.