It said that the decision to guard the Tomb of the Unknown Soldier was a sign of respect to the fallen ones. Below I included a piece I received from a fellow veteran regarding the Tomb of the Unknown.
In 2003 as Hurricane Isabelle was approaching Washington , DC , our US Senate/House took 2 days off with anticipation of the storm. On the ABC evening news, it was reported that because of the dangers from the hurricane, the military members assigned the duty of guarding the Tomb of the Unknown Soldier were given permission to suspend the assignment. They respectfully declined the offer, "No way, Sir!" Soaked to the skin,marching in the pelting rain of a tropical storm, they said that guarding the Tomb was not just an assignment, it was the highest honor that can be afforded to a serviceperson. The tomb has been patrolled continuously, 24/7, since 1930.
Hope this info helped..