Check out one of the best, shortest explanations of the gospel by John Stott (1921-2011) in his classic, highly recommended book The Cross of Christ:
"The biblical gospel of atonement is of God satisfying himself by substituting himself for us. The concept of substitution may be said, then, to lie at the heart of both sin and salvation. For the essence of sin is man substituting himself for God, while the essence of salvation is God substituting himself for man. Man asserts himself against God and puts himself where only God deserves to be; God sacrifices himself for man and puts himself where only man deserves to be. Man claims prerogatives that belong to God alone; God accepts penalties that belong to man alone."
“I could never myself believe in God, if it were not for the cross. The only God I believe in is the One Nietzsche ridiculed as 'God on the cross.' In the real world of pain, how could one worship a God who was immune to it? I have entered many Buddhist temples in different Asian countries and stood respectfully before the statue of the Buddha, his legs crossed, arms folded, eyes closed, the ghost of a smile playing round his mouth, a remote look on his face, detached from the agonies of the world. But each time after a while I have had to turn away. And in imagination I have turned instead to that lonely, twisted, tortured figure on the cross, nails through hands and feet, back lacerated, limbs wrenched, brow bleeding from thorn-pricks, mouth dry and intolerably thirsty, plunged in Godforsaken darkness. That is the God for me! He laid aside his immunity to pain. He entered our world of flesh and blood, tears and death. He suffered for us. Our sufferings become more manageable in the light of his. There is still a question mark against human suffering, but over it we boldly stamp another mark, the cross that symbolizes divine suffering. 'The cross of Christ ... is God’s only self-justification in such a world” as ours...."