I deleted User:Tordmor's explanation because I don't see anything in the 2nd through 10th commandments that mentions the exodus, so I don't see how the 1st commandment sets that up as a theme for what follows. In addition, its mention here comes across less as "I set you free; aren't I a great guy?" and more "I set you free; now you owe me", IMHO.
In addition, I see no indication that the "other gods" would enslave their followers. I think that part of the commandment is adequately explained by positing that YHWH (or his priests) don't like competition.