The gospel is not just a good idea or good advice. The gospel is the good news about what God has already done through Jesus Christ. https://www.desiringgod.org/messages/god-in-christ-the-price-and-the-prize-of-the-gospel/excerpts/the-gospel-in-six-truths https://www.desiringgod.org/messages/god-in-christ-the-price-and-the-prize-of-the-gospel