Chain lube is for the contact between chain and sprocket teeth, where the grease sealed around the pins cannot reach. 
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Not quite correct. A (well maintained) roller chain does not show significant sliding motion between the rollers and the sprocket. That was Mr. Reynold's ingenious invention. The roller (as the name suggests) rolls in and out of the sprocket as it engages and disengages. The sliding motion (and a significant amount) happens between the roller and the bush, this part of the chain (in an o- or x-ring chain) is NOT sealed.
The lubrication between the roller and the bush is needed and crucial for the functioning and long service life of the chain.
Since it's a rather small space between roller and bush your chain lube has to be of very low viscosity when you apply it. Something called "capillary effect" will suck the lube into the space between roller and bush.
Once the lube is in there it should solidify into a thick greasy consistency to make sure it stays in there for longer instead of being thrown out by the centrifugal forces from the chain running around the sprockets and flung off.
If you do not lube the rollers they will quickly seize and stop turning on the bushes. Now you have sliding motion between the rollers and sprocket as the chain engages and disengages the sprocket and the rollers and sprockets will wear rapidly.
The o-ring or x-ring seals only seal the space between the bush and pin. This is where the chain links pivot relative to their neighbours to move around the sprockets.