Happiness:
Wanting, and working towards, a Mercedes Benz. We achieve it, and it's actually in the driveway. We're happy.
Joy:
We don't get the Mercedes, and question ourselves if it was all that important. We realize and accept that all along, Jesus wanted us to be serving others more and ourselves, less. And that, in the end, there's greater satisfaction for doing so. That's joy.
On life's "built-in misery," there are many factors that have us believing this. For one, there's church and religion suggesting or telling us that we'll only have peace when we die.
But God, according to Scripture, didn't mean it to be that way.
In the beginning, He said on the 6th day that everything He had created was "very good." He provided Adam and Even paradise or, as I interpret it, "heaven on earth." (note: I'm just accepting Genesis and not getting into the common debate about its credibility).
When John the Baptist said "repent, for the kingdom of God is at hand," did he mean only when people die, or when people are still alive on earth? Doesn't "at hand" mean now, if we accept Jesus? Wouldn't it seem like a waste if God created us only to suffer on earth, and gain a heavenly existence only when we die?
All the evidence from Scripture suggest that it's not the case. The biggest proof is that Jesus came and gave - actually, reminded - us that there's a recipe for experiencing heaven, or joy, on earth. And that's to love Him above all else, and to unconditionally love others as ourselves.
When we carry out that calling, we experience joy ("heaven on earth"). How about the rest of the world that "lives in misery?"
Let's recall that Jesus asks us then to spread the good word and "make disciples of all men."
That said, it seems quite clear to me that as believers and followers of Jesus, each one of us needs to experience true joy by living His word everyday, and then to spread that joy by interacting with people. So that the world will begin to see His original plan for us.
Seems reasonable? Please share when you're ready.
