Why would President Madison want movable sidelights on either side of these grand doors?  The answer appears to be ventilation.  Even when the doors are closed, if the sidelights are open, breezes can freely pass through the Entry and on into the Drawing Room.  Capturing all possible breezes was an important part of house design in Virginia during the 18th and 19th centuries and without a large amount of ventilation, the hot, non-air conditioned summers were miserable.  Going to the trouble and expense of having movable sidelights instead of just opening the doors also suggests that the Madisons wanted to maintain a sense of privacy in their household.  Because Montpelier was often filled with guests and was serviced by multiple slaves, being able to comfortably shut off the Drawing Room from the low-grade pandemonium that undoubtedly characterized the plantation on a warm summer day must have been a treasured luxury.