slayerangels:

gemwrites:

So Castiel, a mere
seraph, is able to get in Lucifer’s way and stop him when Lucifer wants to kill
Sam. This seems pretty damn impressive to me. Lucifer is an archangel, “Heaven’s
most terrifying weapon,” yet Cas stops him dead in his tracks when Sam is
threatened. What might Cas achieve if Lucifer tries to kill Dean at some point?

Sam took control over Lucifer too in Swan Song when he saw a toy soldier in a car.  And he’s a ‘mere human’.  It can’t be all that difficult honestly.  But, Cas being an angel, it would be easier for him that it was for Sam so, yeah, not that difficult.