I really like The Drumhead from TNG. It establishes the nature of Star Trek at its most essential. It’s mostly a talking episode, although there’s some action with an explosion, which is perfectly average to me. It gives you a feel of the dynamics of some of the politics in the universe, which I think is a great way to get people involved. It’s got one one of those great Picard speeches that puts a badmiral in their place, solving the problem non-violently. It’s also a great parallel to any slippery slope security tightening after a major event happens, which is basically always a timeless message of avoiding overreaching authoritarianism at all costs.
Another TNG one I’d pick is probably The Ensigns of Command. It’s another example of an episode that’s mostly talking, a little bit of action, with a non-violent resolution. It’s fun watching Picard come up with inane legal bullshit to deal with the very strictly by the books alien species, satisfying their requirements in a way that meets his agenda while also being within the rules.
Honestly, I could rationalize different episodes all day, but since those were the first two that came to mind, I’ll just leave them at that.