how is it not interesting?
vader is established early in the film as obi wan's former pupil and the exterminator of the old jedi knights. he is also 'established' as the man that that killed luke's father.
our first introduction to the lightsaber is in obi wan's cave, it's given a sense of wow and wonderment before we ever even see it in action. remember before 1977 no one had seen one before. watching luke ignite the saber for the first time is still a legendary moment.
keep in mind the audience didn't know that vader had his own saber as well. so when obi wan is making his way through the death star and sees this...
this might be the single most "shyt just got real" moment EVER.