A few people have collected definitions of 'The gospel', most notably Trevin Wax, but also recently Rachel Held Evans (members of different tribes and quite interesting to compare definitions). I also enjoyed David Keen's musing called Firing a gun in the air about this question of the gospel and what it means when we preach it 'right'.
At times as a Pastor, I am learning that sometimes your best efforts, your most passionate preach of 'the gospel', your most fervent prayer and your deep and heartfelt sacrifice seems to achieve so very little in the lives of others. At least on the face of it. As the I thought about all this, I was reminded of some words Frederick Buechner wrote that gave me comfort and solace. Somehow, I seem to need them today:
"Stop trying to protect, to rescue, to judge, to manage the lives around you . . . remember that the lives of others are not your business. They are their business. They are God’s business . . . even your own life is not your business. It also is God’s business. Leave it to God. It is an astonishing thought. It can become a life-transforming thought . . . unclench the fists of your spirit and take it easy . . . What deadens us most to God’s presence within us, I think, is the inner dialogue that we are continuously engaged in with ourselves, the endless chatter of human thought. I suspect that there is nothing more crucial to true spiritual comfort . . . than being able from time to time to stop that chatter . . . "
If you want a good listen then 'What is the gospel?' may do you well.