As far as I understand from the forty, or maybe fifty times Steve has said it, "Losing weight requires a debt, gaining muscle requires a surplus", paraphrased.

Most people advocate to lose weight that you do some weight training, a good diet, a little cardio.

I can do that.

Why is, exactly, weight training such a crucial part if I'm trying to lose the weight, though? If I'm not giving my body the necessary calories to gain a good mass of muscle, how is weight lifting still a major part?

I have read a lot of the stickies and a lot of posts, but most of the reasoning seems to lay in "you're gaining muscle".. but then I thought I needed a surplus to gain a decent amount of muscle.

So the cycle of confusion.

Weight training will provide a strong stimulus to maintain the muscle you've got. When you invoke an energy deficit, you lose WEIGHT. Weight is comprised of not only fat, but muscle. How much muscle you lose depends on a host of things such as diet, body fat level, exercise, genetics, etc.

Also, people seem to lump all 'fat burning' exercise into one category: And that category is that of anything that elevates your heart rate for a prolonged period of time. Namely cardio.

You should rid that notion from your brain.

Lifting weights does burn calories too.