"It was like a load off my mind. Poor bastard—never knew how close he'd come to getting killed. Even if I told him, he would have never believed me."
I'll spare you any of my high-falutin mumbo jumbo on Goodfellas' greatness. We've all seen this great movie. You know it's great; I know it's great. This movie is great. Period. Let's cut to the chase: I love the use of voice-over narration in Goodfellas. Rather than elucidating the plot, it seeks to give us a window into Henry Hill's psyche. It is stylistic rather than functional.
Consider the above quote. In the previous few scenes Henry had been obsessing over Jimmy's plan to whack ball-buster Morrie, thinking of every possible way to convince Jimmy that a hit would be pointless (counterpoint: Morrie's annoying). And then at a poker game with Morrie and the bunch, Jimmy leans over to Henry and tells him that the whacking is off. Henry is relieved; now he won't have to answer Morrie's widow's questions about her missing husband's wherabouts. But you know what happens next.
For some, this voice-over might be a cheap bit of misdirection, but—although it does momentarily lull us into a false sense of security—the intention here is something else entirely: it is the voice-over functioning as a tonal device. Obviously because Henry's voice-over is in the past tense, we know that he is narrating from a future point. Yet, it has the quality of a running interior monologue. We are privy to Henry's thoughts as he experiences everything. For Henry, at that moment, Morrie was saved, never to be whacked. Thus as he becomes relieved, so do we.
Interestingly, with this narration, we see that Henry is not omniscient. He is not privy to all elements of the plot—very rare for a movie that employs voice-over. The narrator is usually our know-all God, guiding us through every intricacy of the story. Here, even our narrator doesn't know what the fuck is going on. Whereas most voice-overs act as security devices ("Don't worry, folks; I won't let you get lost here. I'll explain everything."), here, nothing is safe.