How we cite our quotes: (Book.Chapter.Paragraph)
Quote #1
"The gods only go with you, Cerdic, if you put yourself in their path." (I.8.30)
Merlin mixes metaphors here. Yes, working with "the gods" means that he believes he's just going along with fate. But he also understands that there's a certain amount of free will or self-determination in this bargain. Merlin has to seek power on his own in order to be useful to the god in the future.
Quote #2
"So you came ashore on your own in the middle of a winter's night, and in a strange country, and the god threw you straight at my feet. You and your god between you, Myrddin, make a pretty powerful combination. I can see I have no choice." (II.5.57)
Ambrosius acknowledges that Merlin isn't just being thrown around by supernatural powers; he's also using his natural cleverness to do the work of fate. This is what makes him a truly powerful character, one that even mighty kings will listen to.
Quote #3
"A man takes power where it is offered," he said again. "You have told me you don't know what god has his hand over you; perhaps Mithras was the god in whose path you put yourself, and who brought you to me. We shall see. Meanwhile, he is still the god of armies, and we shall need his help." (II.6.23)
Ambrosius gives Merlin a soundbite to live by: take power where it is offered. That leads Merlin to some shady people and places, but it definitely gives him the chance to learn all kinds of useful things. And it's true that half of Merlin's magic comes from his knowledge and his continual seeking of knowledge. The rest, of course, comes from some unknown supernatural source.