Going out for a walk is generally considered as a healthy and positive habit.  But in the essay Max Beerbohm takes a contrarian view.  He brings the readers' attention to a major disadvantage of walking for walking's sake.

He begins the essay by saying that he has never gone out for a walk.  He has been taken out for walks.  In London, nobody compels one to go out for a walk. But while living in the countryside, when an acquaintance invites you for a walk it is difficult to escape.

The objection of the author against walking for walking sake is that it stops the brain.  Here the author is questioning the general belief that walking is good for the brain.  A person with power to instruct and amuse loses these qualities when he is out for a walk.  In the place of his intelligent remarks while inside the room, he now starts flattering the friend and his relatives, and starts reading aloud whatever he sees on either side.  He even reads traffic signs and milestones.  

The author explains the reason in a hilarious way.  He says that when one decides to go out for walk there is a struggle between his brain and soul.  Brain demands a reason for going out but soul has none to offer except self gratification.  Brain suspends this to tomfoolery goes to slumber.  It wakes up only when the person is back inside the room.  

Beerbohm says that he is not totally against exercise.  In moderation, it is good for health.  But in principle he is against the idea of walking for walking's sake.