Heaven is the realm of our rejoicing. If we are earthly minded our rejoicing will be temporal at best, non-existent at worst.
The problem with heaven is that it is THERE and we are HERE. How can we who are HERE rejoice in what is THERE?
I think this is tough and is why heaven gets so little air-time in our theology. We know we are to set our affections on things above, but things above are not seen, so soon our affections are drawn to what we can see.
“Hey, that guy Moses who brought us out of the wilderness, he’s been gone for a couple weeks, let’s go worship some golden cows.”
“Dude, sweet idea.” and off we go.
We laugh at goofy Aaron and the Israelites, yet we do this all the time, just not with golden cows, but with plastic Apples (this is a reference to the various iProducts produced by the Apple corporation that everyone has their face in and is intended to be a joke with some truth and applied much further than merely Apple products). (Jokes that need to be explained are not funny.)
Heaven is like Christmas for a kid. I remember many a Christmas Eve having a hard time sleeping. Looking at presents under the tree for weeks beforehand, even popping some tape off to see if I could get a glimpse at the package inside without mom and dad finding out.
“Anticipation is better than gratification” my parents always told me. They also told me lima beans taste like candy.
But in many cases anticipation is what makes the gratification worth it. Heaven is our anticipation, it is our hope, our hope of God’s glory fully revealed and reveled in that causes us rejoicing now.
Don’t even try to give me this, “Oh, but we can have heaven on earth” business, because we can’t. If we could, then all the promises of heaven and its hope are meaningless. As we convince ourselves heaven can be on earth, we talk less about heaven and fixate on materialism (see American Christianity).
We rejoice in hope and hope maketh not ashamed. Whatever junk life throws at us, our eyes are on heaven, and since heaven is our real expectation, we are filled with rejoicing.