This episode is an examination of the parent/child relationship. The emphasis is on mother/son, but Giles and Buffy represent father/daughter, and perhaps even Buffy/Dawn as mother/daughter, and how these relationships affect who you are.
I love the first flashback, seeing child Robin being told he was not as important to his mother as the mission was. We later see flirting with Buffy again, commenting on how she reminds him of his mother. He's attracted to her because of those Slayer qualities, very much as Spike is.
We go to Giles and Buffy in the school. I think Giles' demeanour and the location are important to remind us of their teacher/child relationship, which disintergrates as Buffy forcefully disagree with him about Spike.
When Giles uses the Prokaryote stone on Spike he pronounces it 'procreate' and later Buffy calls it the 'prophylactic' stone which made me smile. I also like that Buffy runs to Spike when he's in pain
The next flashback shows the closeness between Anne and William. She praises him, they obviously love each other, though there is some gentle flirting there. He sits on the floor at her knee, like a child, not on the couch as an adult would. She sings to him, as you would a child.
When Spike is triggered, he accidentally hurts Dawn and suggests Buffy should go look after her (as his mother would have him) but more like Nikki, Buffy says 'She'll be okay. She's tough', but we see she isn't, that she has been hurt and it's Willow who is tending to her. Buffy later admits that she would sacrifice Dawn if it meant saving the world and it's only later, when the mission is complete, that she checks in on a sleeping Dawn.
The third flashback shows Spike sitting on the couch like a grown-up, kissing his second mother. Dru is not happy that William wants to bring his mum with them

He believes he is doing the right thing in turning his mother, he believes he's doing it out of love and his continuing need to have her near.
Buffy totally diregards Giles and releases Spike. She refuses to listen to him. Robin steps in, and convinces Giles to go along with his plan to dust Spike. Giles says 'Buffy would never allow it', he realises he has little power in their relationship now and I think that knowledge is what forces him to go along with Wood.
BvVS has told us repeatedly that vengeance is a bad thing. Revenge never makes anyone feel better, achieves little, and often makes those looking for revenge feel worse. But Spike and Wood have to fight. It's the only way for either of them to come to terms with their past, for Robin to find some closure and for Spike to understand the trigger, and for both of them to free themselves from their pasts.
The last flashback is Spike killing his mother again. But she's no longer truly his mother, as he comes to determine that she is just the demon and he doesn't have to believe the things she says to him.
I love that Spike says 'I know Slayers' and Buffy confirms the truth of this when she says 'I have a mission to win this war, to save the world. I don't have time for vendettas. The mission is what matters'. And to be honest, I agree with her. Nikki would be so disappointed in Robin here, why is he wasting his time on revenge, when they have a war to fight.
By the end of the episode we see that Giles has finally got the General he wanted
GILES
Well, that doesn't change anything. What I told you is still true. You need to learn—
BUFFY
(looks at Giles) No, I think you've taught me everything I need to know. (shuts her door)
Great episode that looks at what it means to be a Slayer and how the past can hold you back. You can choose how you view the past and how you let if effect you in the present.