For the same reason Christ ate with tax collectors and other sinners I would imagine, not that the pope is or considers himself to be Christ but rather is making and effort to be Christlike.
I could be wrong;)
*** I could be wrong;)***
Titus 3
"As for a person who stirs up division, after warning him once and then twice, have nothing more to do with him, knowing that such a person is warped and sinful; he is self-condemned."
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