Everyone likes to link their political agenda to the message of a popular pope, but Bernie Sanders is really leaning into the most radical elements of Pope Francis's preaching in order to help bolster his case that the country needs a dramatic new direction in policy rather than the kind of continuity with the Obama administration that Hillary Clinton would represent.
This element of radical anti-capitalism in the pope's preaching has deep roots in Catholic Church doctrine but has, naturally, not been welcome in conservative circles.
But it also highlights a bit of a tension in Sanders's own thought. He's a self-described democratic socialist, but in most of his policy prescriptions he doesn't seem to be actually calling for the nationalization of industry. When Ezra Klein asked him what socialism means to him, Sanders essentially described the generous welfare states of Sweden, Denmark, and Finland as his goal.
There's a big difference between where those countries are and where the US is, in terms of the level of taxation, the generosity of the welfare state, and simply the quality of public agencies. But a Nordic welfare state is really not this kind of entirely new non-capitalist society that Sanders and the pope are talking about.