Until Roger Ebert discussed that point a couple of decades ago, I never caught the relevance either. But it's appropriate and makes great sense when we've just left the Moonwatcher character becoming the first homo sapien killer.....after being influenced by the Monolith. The monolith's purpose as I see it is to induce evolution, and the only way to facilitate it is for man to discover violence in order to survive as well as evolve. So Kubrick jump cuts from Moonwatcher's spinning bone-weapon to another slowly floating weapon (or arsenal of weapons in space). Now do you see why I find this film poetic?
Other than that above plot point, Maurice did a better job answering beamMe's last question than I possibly could, and also brought up two points I've never considered. He noticed the Heywood Floyd section has no title card. And he noticed the Discovery resembles Moonwatcher's thrown bone. Maybe now we know why the immense ship is shaped as it is. Yeah, I know, it's also kinda shlongy, but so are old Klingon ships.
Title cards notwithstanding, I always think of 2001 as THREE parts instead of four: the Moonwatcher incidents, the Floyd mission, and the two-part Bowman adventure. I think it's also the recurring appearances of the Monolith(s) that make the film poetic. We can see how the Moonwatcher evolves, and we know Bowman is evolving in a more positive way. Floyd never evolves. I don't consider him a closet Neanderthal or anything, but the ending of his segment to me is the most confusing and disorienting. The Monolith (or another hidden source) emits one hell of a sonic signal which prevents Floyd's team from taking a photograph of it. Here's one moment where I'm not certain of the overall meaning. And when you see the way it ends, you tend to wonder if the team survived that ear-solitting moment because they're never seen again. Floyd is heard again after HAL is deactivated, and his name is seen in teeny-tiny type. It might be too small to notice on DVD though.