BEARINGS 101
Bearings sit in the wheel hub and are what allows the wheels to roll in the skates.  Many bearings reference the ABEC rating they fall into.  It is a standard that all bearing manufacturers (not just the roller industry) use to determine the tolerance range of a particular bearing.  This rating has nothing to do with bearing quality!
 
Bearings consist of Races, Balls, Cages and Shields.  Carbon Steel races will roll freely if there is no pressure on them.  But after a few uses, they tend to slow the bearings.  Better quality Chrome Steel races will have a tendency to roll freely over the lifetime of the bearing.
 
Remember, how fast you roll depends on you and your ability.  Higher rated bearings will not make you go faster BUT you will have more roll out.  Roll out is how long it takes for the wheel to stop spinning.  Higher quality bearings will spin longer after you stop pushing.
 
Finally, lubricants keep the metal parts from wearing against one another and keeps dirt away from the sensitive inner parts.  GREASE lubricants are thicker, act as a seal against dirt and requires little servicing.  However, it can increase torque and slow down the bearing.  OIL lubricants are preferred for better roll but are susceptible to dust and contamination.  An oiled bearing will require attention to keep them in good working order.  Always use a lubricant and cleaner that is specifically designed for bearing use.  Household cleaners will do the job but will result in slowing the bearings down.