It's the most famous passage from the Bible, "For God so loved the world that he gave his only Son, that whoever believes in him will not perish, but have eternal life." It's the entire message of the gospel boiled down into one sentence.
But why would we just leave it at that? Why not expand on it to show us that this verse is more than a summary of Jesus' message. The passage tells us some particular things about God.
We see that God's motivation to save the world is his love. He loves us so much that he was willing to give up everything, even his only Son, to save us. That sounds a lot like one of the parables that Jesus used, the parable of the treasure in the field.
God sends his son to save us so we would not perish. It's like when the coast guard shows up to save a bunch of drowning people. They throw out the life preservers so they can be pulled to safety. Jesus comes to dying people who are trapped in sin, and he offers us salvation.
There's more to it, of course, but you'll have to listen to hear it all!