In the Gospel of John, the love God has for the world leads directly to the offer of eternal life. In Matthew, Mark and Luke, the same offer is made, but the wording is different. The offer in those Gospels is citizenship in the "Kingdom of God" (Mark & Luke) or the "Kingdom of Heaven" (Matthew). Same offer -- different words.
Now, using "Kingdom" at all is a bit of a risk for Americans living in 2011. Such language can carry ideas of oppression, domination or slavery. America was birthed out of the rebellion against such things. Consequently, we don't much care for kings or for kingdoms.
But when you read how Jesus talked about God's kingdom, it doesn't sound much like the thing we're afraid of. In fact, he once told people that such thinking was upside down. Rulers in the Kingdom he came to initiate would be servants. First in line would be last and vice-versa (see Mark 10:42-45).
Jesus, who was the most rightside up person to ever live, says we've got our notion of what a real King looks like backwards because we've only seen the way the ideal has been perverted by fallen, greedy humans. Without abandoning our terminology, Jesus comes to redefine those terms so we can better understand what he's about. He will be King, but he will be unlike any King we've ever had before. He'll have all the good parts of being King with none of the bad parts.
This is nearly impossible for us to fathom. But it's true.
I think it is precisely because we've misunderstood the idea of King and Kingdom that Jesus' message is so often misinterpreted as bad news instead of good.