For God so loved the world

And as Moses lifted up the serpent in the wilderness, even so must the Son of Man be lifted up, that whoever believes in Him should not perish but have eternal life. For God so loved the world that He gave His only begotten Son, that whoever believes in Him should not perish but have everlasting life. For God did not send His Son into the world to condemn the world, but that the world through Him might be saved. – John 3.14-17

If there was only one verse we could have to explain the gospel it would have to be John 3.16. Growing up in the American South it is a verse that we would hear and see everywhere. It is the first verse that many Americans ever learned, even if they were not saved. You can't miss in in the culture . The reason I think is that it was such a clear and simple presentation of the truth. Its all there.

For God – that’s where it has to start, with God, not us
So loved – God is love. He acted in love. What He here is because He is acting in accord with His nature.
The world- that pretty mush says it. I certainly do not know all about how predestination works, but I do know that God loves His creation and the people who fill it. He knew the world was living in darkness without hope.
That He gave – a gift. He did not give a payment or a reward or anything of the like. He gave a gift.
His only Son – I also don’t understand all of how the Trinity works. But in some way God the Father sent God the Son because He is the only one who could pay the penalty for man’s sinful state. The penalty for sin is death, but the sacrifce has to be sinless to pay it.
That He who believes – believes, not does good work or acts religious
In Him – faith in Christ alone
Will not perish – will not have to suffer eteranl death. Bodies will die, but we will live on.
But have eternal life – always, eternal, forever, unending life

There it is. The plan and way of salvation is one small verse.

Now, what are we going to do with it, keep it or share it?