HOUSTON, TX—Portfolio diversification: It’s a basic principle of investing. Unfortunately, many Christians believe they’re supposed to put all their treasure in Heaven, which simply is not smart investing. Pastor Joel Osteen, though, is promoting a stronger portfolio. “Treasure in Heaven is pretty good, because there rust and moths can’t get it and thieves can’t steal it,” Osteen said. “But there’s a big disadvantage to that treasure: You can’t exchange it for a Ferrari or a mansion—not an earthly one, at least, like I got, and it is glorious.” Osteen wants Christians to remember that eternity is a while away (hopefully),...