The Bible's purpose is not so much to show you how to live a good life. The Bible's purpose is to show you how God’s grace breaks into your life against your will and saves you from the sin and brokenness otherwise you would never be able to overcome... religion is 'if you obey, then you will be accepted'. But the Gospel is, 'if you are absolutely accepted, and sure you’re accepted, only then will you ever begin to obey'. Those are two utterly different things. Every page of the Bible shows the difference. – Tim Keller
Grace changes everything.
You are far worse than you dared to imagined, and you are far more accepted than you dared to dream. Jesus' death on the Cross is the centerpiece of the Gospel.
Where does this word come from? The Greek term "gospel" (eu-angelion / good news) is the #1 difference that sets followers of Jesus from followers of any of the other world religions. In olden times, when a king went off to war, the people of his city would sit and wait for news. If a herald would come and shout with joy, "Our king has triumphed!" then the city would celebrate and throw the gates open to welcome the victorious army. If the battle did not go well for the king, he would not send heralds. He would send military advisors. These men would shout a warning, "The king has lost and is retreating. Man your battle stations!" If this happened every able bodied person would work to defend the city, or would flee into the country side.
Many spiritual journeys look like the second situation. People work hard, or flee, because enemies larger than themselves are bearing down. Death and disease, crisis and conflict, wars and worry - we man the walls, pick up our weapons and try to hold these off. Followers of Jesus know the truth. The battle has been won, and even though we didn't lift a hand to help, we gain the reward.
This means that the Gospel is not about what we have to do. It is not advice. The gospel is news of what God has already done. When Jesus yelled, "It is finished" it really was!