Eternal life is represented by an obelisk.
A monument with two pillars symbolizes the passageway into the next life.
W B Porter Jr, who died 07 May 1881 at the age of 36, is interred under an obelisk. One can assume it was his family’s hope that he was granted eternal life.
W B Porter Sr died four years later. Two pairs of pillars on his monument make me think he hoped the passageway to join his son would be open from every direction.