Shawn has recently died. He was shot twice in the chest. His mother is in disbelief. He was on the way to get his mother's "special soap" for her eczema. The significance is it the catalyst for fueling the fire in Will getting revenge for his brother.
"...the only big brotherShawn had ever had." Will has now seen Buck walk into the elevator. He seems to be real but Will doesn't know. Buck is wondering what Will is going to do with this gun. Will informs him he is going to follow the rules and kill the man who killed his brother. Buck doesn't believe he will do it. This shows how the ghost of Buck is trying to give him a wake up call that he is not ready for this life.
RIP BUCK YOU’LL BE MISSED 4EVA
On the 6th floor Will meets another person. A cute girl his age. He ends up finding out that he used to play with her and she was shot. She is concerned with the gun he has : "What you need / a gun for?" This shows the significance of the gun. The only thing that could be more powerful than your words. A gun can end someone's life and that is in the hands of somebody else. The ghosts showing up are trying to persuade him not to do it.
The next floor the elevator stops at is the 5th. The next person to walk in is Mark. Which is Will's father's brother, so that makes him his uncle. The significance behind this is another way to convince Will not to go through with killing Riggs.: "He continues for nine blocks,gets to Riggs’s house, sees Riggs,pulls the gun out, and . . ." Mark was killed on the corner . He tells Will that Rules aren't always the answer to someone getting killed. It just gets you in more trouble.
On the 4th floor, WIll's father walks in. Will is very surprised. He hasn't seen his dad in about 12 years. The significance of this is to teach Will a lesson. He doesn't have to follow the rules because it will always end up bad. His dad showing up is like a parallel to what will happen to Will: "He pulled the gun from my waistband. / And put it to my head."
The next person on the elevator was someone named Frick. Frick is recognized by Buck, Frick killed Buck. He tells Will think you know the killer doesn't mean it is the right person, "NOW LET ME ASK YOU / how you know / this kid Riggs got your brother?" This proves how Shawn avenged for Buck's death and got the right person, but how does Will know Riggs is Shawn's killer.