Oh I like the way your are thinking....

So you labor, make something, exchange that for money and then buy the tractor. The tractor making people get your money in exchange for their tractor constructing labor. In this regard folks are just exchanging the product of their own labor.

But if you start renting the tractor out is that the same? In some sense the tractor is a substitute for the product of your effort (you traded grain for money for tractor) so if you were to trade the tractor for, say beer, its still just a swap. But if you are renting the tractor, you get something from the renters but you still have the whole tractor back at the end. You got something from them just for having had ownership of the tractor.