He specifically says "do not underestimate the powers of the Emperor" translates to "Don't get taken prisoner and try and face off against two of the most powerful Sith in history alone."
He probably imagined that Luke would defeat Vader, then train more Jedi and eventually defeat Palpatine. Thus the "pass on what you have learned."
Also I think in the ROTJ Novel Luke does deflect Palpatine's lightning bare handed before getting overwhelmed.
Luke doesn't deflect it, he attempts to absorb it and while initially he's partially successful, he fails utterly at stopping Palpatine when he ramps the intensity.
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for the exact same reason he didn't warn the other Jedi of their impending deaths.
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Shadilay my brothers and sisters. With any luck we will throw off the shackles of normie oppression. We have nothing to lose but our chains! Praise Kek!
THE MOTTO IS "IN KEK WE TRUST"