Eminem claims his music can be used as a therapy or treatment for those who are constantly struggling or going through challenging times in their life.

Eminem also touches on this subject in “Sing For The Moment,” explaining how kids/teenagers listen to this music to help them get through tough times, ultimately using it as a form of therapy.

Or for anyone who’s ever been through shit in they lives
So they sit and they cry at night wishing they’d die
‘til they throw on a rap record and they sit and they vibe

http://rapgenius.com/discussions/49333-Eminem-has-nothing-left-to-prove

Yin and Yang represent the two opposite principles in nature. In this case the two opposing principles are people breaking the law by ‘slanging’ dope (selling drugs) to pay for their bills like a law abiding citizen. To do this would simply be a contradiction, thus being their yin and yang

Meech claims his unique flow is classic like the record scratches of DJ Premier.

DJ Premier is a hip-hop producer and DJ that is universally considered as one of the all time greats in hip-hop culture. In addition to his amazing beats, DJ Premier is also known for his signature classic scratches, in which he scratches lyrics from several different songs to construct new phrases. These are often used for his choruses.

Meech alludes to the idea that not everyone is perfect, and we should embrace what we see in the mirror despite our flaws or insecurites as they ultimately determine who we are. Everybody is different, and what we see in the mirror gives us our own unique identity.

To prosper is to succeed in material terms or be financially successful. In reference to the previous line, Meech is saying that the very same ‘friends’ that doubt you while you are pursuing your dreams are the same ‘friends’ that will be asking you for a hand-out once you succeed despite them doubting you.

Referring to the first single for The Marshall Mathers LP 2 “Berzerk”, which samples Billy Squier’s “The Stroke”.

http://www.youtube.com/watch?v=C_OGARBe6W0

Matthew Mitchell felt a strong connection to his music and their shared initials just add to the creepy connection he felt with Em.
It’s also worth mentioning that before Infinite, Eminem went by the name M&M.

Stan’s brother is mentioned by first name in the original song.

(…) you coulda signed an autograph for Matthew
That’s my little brother man, he’s only six years old

This line also supports the idea that the song itself is about his past catching up to him. Despite where Eminem finds himself now, Matthew is a symbol of the past that Eminem can’t escape. The idea that a character from one his most critically acclaimed songs is killing the present-day Eminem is symbolic of how his new music is always going to be compared to his first albums.