Suppose that Jesus had never come, that God had merely sent an elaborate love note. What difference would that make?

They were terrified and asked each other, “Who is this? Even the wind and the waves obey him!”

~Mark 4:41

This is a very interesting question.  I think that this world would have been very much different today than it is.  Usually, if we recieve a note from someone that may proclaim how much they love us, in very great deail, and there's a chance we don't even know who that person is, we might say to ourselves "oh really?"  It doesn't mean that the letter isn't necessarily good enough, but it is probably better if we find out the truth from the very person that sent this letter.  This is why God sent us Jesus so that way we would have no excuse to doubt what He was trying to tell us.