In simple terms, justice can be seen as getting or giving what one deserves. Mercy removes the punishment which one deserves for one's wrong acts. Grace overtakes mercy by not only removing the punishment one deserves, but by also giving a blessing which one does not deserve. In the context of the Gospel, it means that if God applied justice, we would all deserve to be punished. But God showed mercy in that Jesus took our punishment in our place. Grace means that not only has our punishment been taken away, but God has also blessed us with adoption as His children, and an opportunity to grow into His nature and enjoy fellowship with Him through eternity.
The modern 'gospel' comes short of the true Gospel in many ways. This false gospel first of all does not tell us what we deserve according to God's justice - eternal death as punishment. As a result, we are not likely to appreciate the generosity of the mercy God is willing to show us. Then we tend to take for granted all the blessings God gives us, thinking we more or less deserve them.
With this kind of thinking, it is only natural that people are not really motivated to love God, surrender themselves to Him in gratitude, serve Jesus by obeying Him in everything and making every effort to tell others about Him. 'Pep talks' are not enough to sustain people's interest in the things of God. It turns out that the things that keep people in churches are the activities, entertainment, friendships and social benefits. But such things feel hollow after some time. Is this what Jesus died for?
It is not that people have no knowledge of the truth. But for many people, truth has not penetrated into their hearts when teaching is merely intellectual. A lot of preaching is unable to make people tremble before God and then rejoice at the good news of salvation. People have not seen themselves as sinners who need a Saviour to save them from their sins. Nobody has told them what punishment they deserve for their sins. They have not understood that receiving forgiveness of sins while they are continuing in their sins cannot really be salvation from sin. Preachers have omitted leading people to true repentance, but instead shown them a shortcut of easy-believism. Prophets are going around comforting people with promises of great things to come without warning them to turn away from their folly and sin.
Why is it that false gospels attract such a lot of people? It is because the preaching of the true Gospel is very rare. It is when we are familiar with genuine currency that we can detect counterfeit notes. But when preaching is not clear about biblical truths, people get deceived with false quotations from the Bible and impressive preaching.
The irony of the situation is that when there is more Bible knowledge than ever before, yet a large number of Christians have not even understood the basic Gospel. God wants those who know the truth to be bold and clear in its proclamation (2Ti.4:1-4).