A crisis of conscience and faith stands at the center of “Roman J. Israel Esq.,” the new film from writer-director Dan Gilroy (“Nightcrawler”), which makes it a tricky sell for mainstream audiences used to movies that sprinkle such lofty debates amidst a cavalcade of thrilling action sequences that speak louder than the drone of words. It seems Gilroy was banking on the idea that a recognizable star like Denzel Washington might be the spoonful of sugar capable of making his medicinal and quite bitter pill go down a bit easier and a heaping dose of Washington, in decidedly low-key eccentric mode, propels this quirky character study a long way. Playing a principled legal savant with a low threshold for social engagement, Washington creates a modern-day Don Quixote or, better yet, a criminal justice version of Cyrano who just can’t face an unloving and sadly uncivil world.