The genuine Gospel is simple.
For God so loved the world, that he gave his only Son, that whoever believes in him should not perish but have eternal life. John 3:16
That is the Good News, but most people simply don't understand it. It is very Good News to anyone that respects the severe and arduous reality of the Old Testament Law (Matthew 5:17-20), and the easy way to escape it. Jesus does not want anyone to "perish" for their sins, but welcomes "whoever" into His Kingdom just because they believe. If we believe, He has good work prepared for us (Ephesians 2:8-10).
But many people think they need to be good enough to get to heaven. Paul preached Jesus's Gospel, but soon people wandered away from it...
I marvel that ye are so soon removed from him that called you into the grace of Christ unto another gospel: Which is not another; but there be some that trouble you, and would pervert the gospel of Christ. But though we, or an angel from heaven, preach any other gospel unto you than that which we have preached unto you, let him be accursed. As we said before, so say I now again, If any man preach any other gospel unto you than that ye have received, let him be accursed. Galatians 1:6-9
The Apostles, the Early Church Fathers for hundreds of years, plus the Catholic, Orthodox, and many other protestant churches to this day, all agree that if you believe, you will be saved. This is the only way (John 14:6, Acts 4:12). Everyone should understand how serious this is. There are many religions and Christian cults that say we must work our way to heaven, but Jesus says we must believe (Matthew 28:18-20, John 3:18, 3:36, 5:23, 8:24, 10:9, 17:3). Jesus talked about hell far more than heaven, so no one should claim salvation isn't important.
Jesus's Gospel says we don't have to worry about whether we are saved (e.g. John 6:47, Romans 8:38-39). Another Gospel says you have no idea, so you better prove it. An honest person would have doubts as to whether they were working hard to be "good enough" just to end up in hell (for no apparent reason). But this game quickly gets cynical, and people think they can cheat God. Being "good" means you have to dress like one of them, talk like one of them, do what they tell you to, and (of course) put money in the offering plate. If you are tired of being unsure, then you need to become one of the church leaders, even become ordained. Then you get to put on their robes so that everyone will tell you how "good" you are. But Jesus had very hard words for people like that:
They tie up heavy burdens and lay them on men’s shoulders, but they themselves are unwilling to move them with so much as a finger. But they do all their deeds to be noticed by men; for they broaden their phylacteries and lengthen the tassels of their garments. They love the place of honor at banquets and the chief seats in the synagogues, and respectful greetings in the market places, and being called Rabbi by men. But do not be called Rabbi; for One is your Teacher, and you are all brothers. Do not call anyone on earth your father; for One is your Father, He who is in heaven. Do not be called leaders; for One is your Leader, that is, Christ. But the greatest among you shall be your servant. Whoever exalts himself shall be humbled; and whoever humbles himself shall be exalted. But woe to you, scribes and Pharisees, hypocrites, because you shut off the kingdom of heaven from people; for you do not enter in yourselves, nor do you allow those who are entering to go in. Matthew 23:4-13
Doesn't that sound like the worst kind of church? A good church will welcome you without expecting you to serve them, or worship them.
Have you ever said to yourself 'God lets me get away with sin because I work hard for Him'? Or worse, 'God will give me a break because people were sinful to me'? Sadly, many have been betrayed by church leaders (Ministers, Pastors, Preachers, Priests, Bishops...) because they say the same thing. At some level, they think their "good" cancels out their evil. This is called Works Righteousness, or Legalism. Instead, we need to remember that Jesus makes no provision for our fleshly sins, neither in heaven nor on the earth (Romans 13:14, Ephesians 2:3, Colossians 3:1-2, 1 Peter 2:11 etc.). Certainly, these sins are intensely cynical because they are kept in the dark (John 3:17-21, 1 John 1:5-2:6). Jesus wants us to reconize our sin, confess it and change our ways (Matthew 4:17).
Another Gospel is preached with deception. Many churches proudly say they are "saved through faith alone" (Sola Fide). But once you understand this, they will ask you "What do you mean by faith?"
Unbelievably, they have re-defined Jesus's Word to shoe-horn it into the weird philosophy of Fatalism. It is not the Gospel, and it always comes back around to Another Gospel. Augustine brought Fatalism into the Church about 400 years after Jesus walked the earth. Augustine was a follower of a sect of the Gnostics, an infamous heresy that John the Apostle and many of the Early Church Fathers spoke against. Then Augustine converted to Christianity. Though he didn't have Christian training and didn't know Greek (the language that most of the New Testament was originally written in), He quickly became a leader in a church in North Africa.
Predictably, Augustine abandoned the Bible and the Early Church Fathers. In 412 he fell back on his Gnostic heresy, which says that God forces people to believe and go to heaven, or prevents them from believing so they go to hell (for no apparent reason).1 The Good News (that Jesus will happily forgive the sins of the whole world if we simply believe) gets twisted into the Bad News (that He throws babies and believers into hell even though they are without sin; see instead 2 Samuel 12:23, Romans 1:16).
Gnostic leaders are the only ones with the "Secret Knowledge" and so they "shut off the kingdom of heaven from people" (as Jesus said above). So most will not preach the Gospel because they say that is not how people are saved, but they still expect people to be "good" by acting like Jesus (again, this is Works Righteousness, or Legalism).
This man Augustine was certainly not “an angel from heaven” (Galatians 1:8b), so how can we trust anything from someone willing to corrupt a basic fundamental of Christianity? As long as it suited him, Augustine taught Free Will. At other times, he taught Free Will but meant the shady Gnostic idea of Non-Free Free Will. He secretly re-defined simple words like faith (as in Ephesians 2:8-10 above) to mean mind-control. A thousand years later, Martin Luther and John Calvin were big followers of Augustine. They tried to reform the church, but soon their followers fell back on Another Gospel.
It's strange to even talk about Another Gospel. Some people might say 'Christians can't get their act together - why even get involved?' But that's exactly what our Enemy wants us to think. When I was young, I sincerely asked what I needed to do to go to heaven. I was told 'Just make sure you are a member in good standing of our church.' That was Another Gospel. No, to be sure that you are going to heaven, and to be sure you will receive blessings on earth, simply believe Jesus. He knows best how to take things from there.
1. See The Foundation of Augustinian-Calvinism by Dr. Ken Wilson. Based on his research, and Augustine’s obvious use of Gnostic/Manichean concepts in his effort to defeat Pelagius, it is very fair to say that many modern churches are founded on the heresy of Gnosticism. Any doctrine that touches on issues as important as salvation should be carefully examined, and it is also very fair to reject anything that so clearly contradicts so many foundational verses in the Bible (e.g. John 3:16). For a scholarly treatment, see the Oxford Dissertation by the same author, Augustine's Conversion from Traditional Free Choice to 'Non-free Free Will': A Comprehensive Methodology. Ken Wilson. Mohr Siebeck, 2018. To-date, this work has never been challenged in a scholarly journal. See also “The Myth of Pelagianism” by Dr. Ali Bonner. For a quick introduction to this topic, see “Ken Wilson Rebuts James White” available on YouTube.com.