There's no doubt that we are earthly creatures: we spend our days seeking pleasure and avoiding pain. The pleasures of the flesh (and the pain of being fleshy) is the rope binding us to every other creature on this earth: not advanced mathematics, not philosophical discourse, not flame wars on the latest social medium.
Every religious system I know tries to escape from our bodily circumstances, though the solutions vary enormously. Some posit a loving God who will take care of us in the afterlife if we do as he says. Some posit the opposite: a vengeful God who will burn us in the afterlife if we don't do as he says. Yet others are agnostic about the existence of God but look for a special state of enlightenment that comes from strenuous meditation.
However they do it, they are all acutely aware that death awaits us and we need a way out. The Jaya is an interesting alternative to these otherworldly religions. Hell awaits men not because they fail to worship a god, not because they refuse to shut their senses, but because they don't want to have children.
How much more fleshy can you get?
Indeed, in this admonition is a tacit understanding of tapasya itself. We have this idea that meditation is a relaxing activity, "reality unplugged." Tapasya is a lot fiercer: etymologically it's tied to heat. It's the burning up of the body.
Perhaps the Jaya is hinting at a counterintuitive proposition: that liberating knowledge is to be found in the deepest strata of our embodiment, not by looking within the body but by looking with the body.