It has been really good to try to come up with a definition of the term "Gospel." John Newton was absolutely right - God's grace is amazing. When you think about the Gospel from the perspective of God's glory, His love and righteousness, it blows the mind and you can't help worshiping Him. So, here goes with my attempt to define "the Gospel":
The Gospel is God’s good news, whereby He demonstrates His glorious character throughout the universe by creating human beings for relationship with Himself, knowing, however, that we would all rebel against Him. The good news includes God’s provision of all the means necessary through His Son Jesus Christ, to reconcile rebellious humanity to Himself, by judging our sin, satisfying His wrath against us, paying the just penalty for our sin, giving us the faith to trust His complete provision for us, and declaring us righteous and forgiven. In all of this, God displays His glory as He magnifies, rather than diminishes, His holiness, justice, righteousness, goodness and love.
 Eph. 3:7-10: Of this gospel I was made a minister according to the gift of God’s grace, which was given me by the working of his power. 8To me, though I am the very least of all the saints, this grace was given, to preach to the Gentiles the unsearchable riches of Christ, 9and to bring to light for everyone what is the plan of the mystery hidden for ages in God who created all things, 10so that through the church the manifold wisdom of God might now be made known to the rulers and authorities in the heavenly places.
 Acts 17:24-27a: The God who made the world and everything in it, being Lord of heaven and earth, does not live in temples made by man, 25nor is he served by human hands, as though he needed anything, since he himself gives to all mankind life and breath and everything. 26And he made from one man every nation of mankind to live on all the face of the earth, having determined allotted periods and the boundaries of their dwelling place, 27 that they should seek God, in the hope that they might feel their way toward him and find him.
 Romans 3:9-18: 9What then? Are we Jews any better off? No, not at all. For we have already charged that all, both Jews and Greeks, are under sin, 10as it is written: "None is righteous, no, not one; 11no one understands; no one seeks for God. 12All have turned aside; together they have become worthless; no one does good, not even one." 13 "Their throat is an open grave; they use their tongues to deceive." "The venom of asps is under their lips." 14 "Their mouth is full of curses and bitterness." 15 "Their feet are swift to shed blood; 16in their paths are ruin and misery, 17and the way of peace they have not known." 18 "There is no fear of God before their eyes."
 Eph. 2:8-9: For by grace you have been saved through faith. And this is not your own doing; it is the gift of God, 9 not a result of works, so that no one may boast.