Encore

when I come back like Jordan wearing the 45

Obviously this is an ode to Michael Jordan's return to basketball after retirement, which was to be Jay's fate as well. But he's also talking about coming back, wearin the 45, meaning a gun
getsbusy5
Michael Jordan took a break from basketball when his father died and he wore the #45 to honor is father.
93xTilxInfity
"Wearing the 45" is also referring to the fact that if it is necessary for Jay-Z to return following a disagreement he will be carrying a "four-five" which is slang for a .45 caliber handgun.
jwmunson