Half-Life 2 Discussion (Spoilers)

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Remember that dialogue at the beginning of HL2? That one that start with "Rise and shine Dr. Freeman..."? What is all that nonsense mean? I dont get it. Gman is talking about some job, and that my time has come or what...
Anyway I think the mission is to fight off the alien infestation, to liberate earth. Killing Breen was only a sideeffect, as I see. But what's in it for Gman?
I will start the game over again and listen to those Tv commercials Breen made at the start of the game like "Point insertion" and "Our Benefactor". He was talking about we have the secret to live forever, just we must wait. And things like that. Maybe that will clear things a bit...