Populists clash: Trump vs. The Pope

TRUMP AND THE POPE: Right-Wing Populist Clashing with a Left-Wing Populist, by Julio Severo.

Francis does not want a wall surrounding the U.S. and keeping immigrants outside, but the Vatican itself is surrounded 100% by a wall preventing the entry of all illegal immigrants, especially Islamic invasions.
If Francis is worried about immigrants, why does not he take them in the Vatican? Why does not he overthrow the Vatican’s wall and make it clear that all illegal immigrants, especially Muslims, are welcome there?