What makes Good Friday so good?

Paul tells the Athenians as recorded in Acts 17:22-34.

So Paul stood before the Areopagus and said, “Men of Athens, I see that you are very religious in all respects. For as I went around and observed closely your objects of worship, I even found an altar with this inscription: ‘To an unknown god.’ Therefore what you worship without knowing it, this I proclaim to you. The God who made the world and everything in it, who is Lord of heaven and earth, does not live in temples made by human hands, nor is he served by human hands, as if he needed anything, because he himself gives life and breath and everything to everyone. From one man he made every nation of the human race to inhabit the entire earth, determining their set times and the fixed limits of the places where they would live, so that they would search for God and perhaps grope around for him and find him, though he is not far from each one of us. For in him we live and move about and exist, as even some of your own poets have said, ‘For we too are his offspring.’ So since we are God’s offspring, we should not think the deity is like gold or silver or stone, an image made by human skill and imagination. Therefore, although God has overlooked such times of ignorance, he now commands all people everywhere to repent, because he has set a day on which he is going to judge the world in righteousness, by a man whom he designated, having provided proof to everyone by raising him from the dead.”

Now when they heard about the resurrection from the dead, some began to scoff, but others said, “We will hear you again about this.” So Paul left the Areopagus. But some people joined him and believed. Among them were Dionysius, who was a member of the Areopagus, a woman named Damaris, and others with them.