Why is this false gospel so successful?
This false gospel is so successful because it pleases man, builds self and seeks to elevate sinful man to God's level. The false gospel is built on man's natural desire to "do" something toward gaining salvation.
Furthermore, the success of the false gospel is also based on the visible. This is particularly true with the prosperity "gospel," which teaches that you will become wealthy if you follow certain steps. Such teaching appeals to man's ego because we like to be successful, healthy and wealthy. If there is a way to obtain such a position, we will gladly dedicate our lives towards that goal. This is not only the case with the false gospel, but it applies to virtually all other religions.
But true Christianity differs from all other religions. We confess that we are hopelessly lost without Jesus; we recognize that we are sinful by nature, and we confirm and confess that there is not one who is righteous among us. We depend on God's grace. We understand that it is impossible for us to attain the holiness and righteousness God requires. We need the One who has paid the ultimate price to atone for the irreparable damage we have caused through sin. That price was the blood Jesus shed on Calvary's cross. He did not repair us, but renewed us by the power of the Holy Spirit. It is our duty to stress this warning to those who emphasize only one side of the Gospel--peace, joy, love, prosperity, health and happiness--without telling the other side, which includes trial, tribulation, suffering and persecution.