Question: How to explain to a not yet observant relative that asking a non Jew before Shabbos to walk with him on Shabbos and pay for the subway for him isn’t sufficient even if one isn’t swiping the card/pushing the entrance bar, but rather goes through the mechanic door? Is there a problem of riding itself or something else besides benefitting from a non Jew doing melacha in places where tchum doesn’t apply?

Answer: The basic explanation is that it violates the principle of Shabbason, resting on Shabbos. This is aside for the fact that it considered a weekday activity, uvdin dchol.

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