Actually, warm soapy water is a lubricant. There is a barber theory about the shaving brush: The bristles push water against the beard which keeps it wet and therefore the hairs stay softer and easier to cut. Can't swear there's any science to this theory, LOL. Just do what works, eh?

The brush is for working up a lather with the bar soap. You can achieve the texture of shaving cream just using bar soap and a brush (and water obviously).